20. Roasting? How should it be done? Give the philosophy of the process. Frying?
20. Roasting is probably the best method of cooking meat, especially "joints" or large pieces, as by this process the meat is cooked in its own juices. Roasting should begin with intense heat, and be continued at a moderate temperature, in order to prevent the drying out of the nutritious juices, as by this process an outer coating or crust of coagulated albumen is formed. During this process the meat loses one-fourth of its weight, but the loss is almost wholly water, evaporated by the heat. Too intense or prolonged heat will dry the meat, or burn it. Frying is the worst possible method, as the heated fat, by penetrating the meat, or other article placed in it, dries and hardens it, and thus renders it indigestible.
21. What is "Trichina?" How guarded against?
21. Trichina.—It should be remembered that ham, sausages, and other forms of pork, should never be eaten in a raw or imperfectly cooked condition. The muscle of the pig is often infested by a minute animal parasite, or worm, called trichina spiralis. This worm may be introduced alive into the human body in pork food, where it multiplies with great rapidity, and gives rise to a painful and serious disease. This disease has been prevalent in Germany, and cases of it occur from time to time in this country.
22. What part of fish is eaten? What does it resemble? Fish as food for digestion? Fish as a diet?
22. Fish.—The part of fish that is eaten is the muscle, just as in the case of the meats and poultry. It closely resembles flesh in its composition, but is more watery. Some varieties are very easy of digestion, such as salmon, trout, and cod; others are quite indigestible, especially lobsters, clams, and shell-fish generally. A diet in which fish enters as the chief article, is ill adapted to strengthen mind or body, while its continued use is said to be the fertile source of nearly every form of disease of the skin. Some persons are so constituted that they can eat no kind of fish without experiencing unpleasant results.
23. List of vegetable articles? Usefulness of the different vegetables? Strychnia? What further is said in relation to the nourishing and other qualities of vegetables?
23. Vegetable Food.—The list of vegetable articles of diet is a very long one, including the grains from which our bread-stuffs are made, the vegetables from the garden, and the fruits. All the products of the vegetable kingdom are not alike useful. Some are positively hurtful; indeed, the most virulent poisons, as strychnia and prussic acid, are obtained from certain vegetables. Again, of such articles as have been found good for food, some are more nourishing than others: some require very little preparation for use, while others are hard and indigestible, and can only be used after undergoing many preparatory processes. Great care must therefore be exercised, and many experiments made, before we can arrive at a complete knowledge in reference to these articles of diet. Tea, coffee, and other substances from which drinks are made, are of vegetable origin.
24. Wheat? "Staff of life?" White flour? Hard-grain wheats? Bolting? Graham bread?
24. Bread.—Wheat is the principal and most valuable kind of grain for the service of man. Bread made from wheat-flour has been in use for many hundreds of years, and on this account, as well as because of its highly nourishing properties, has been aptly called "the staff of life." We never become tired of good bread as an article of daily food.
The white kinds of flour contain more starch and less gluten than the darker, and are therefore less nutritious. The hard-grain wheat yields the best flour. In grinding wheat, the chaff or bran is separated by a process called "bolting." Unbolted flour is used for making brown or Graham bread.
25. Leavened bread? Unleavened? Hot bread?
25. The form of bread most easily digested is that which has been "leavened," or rendered porous by the use of yeast, or by some similar method. Unleavened bread requires much more mastication. Hot bread is unwholesome, because it is not firm enough to be thoroughly masticated, but is converted into a pasty, heavy mass that is not easily digested.
26. Wheaten bread? Bread and butter? Experiment on the dog?
26. Wheaten bread contains nearly every principle requisite for sustaining life, except fat. This is commonly added in other articles of diet, especially in butter,—"bread and butter," consequently, forming an almost perfect article of food. The following experiment is recorded: "A dog eating ad libitum of white bread, made of pure wheat, and freely supplied with water, did not live beyond fifty days. He died at the end of that time with all the signs of gradual exhaustion." Death took place, not because there was anything hurtful in the bread, but because of the absence of one or more of the food-principles.
27. State what is said of the Irish potato?
27. The Potato.—The common or Irish potato is the vegetable most extensively used in this country and Great Britain. Among the poorer classes in Ireland it is the main article of food. While it is not so rich in nutritious substances as many others, it has some very useful qualities. It keeps well from season to season, and men do not weary of its continuous use. It is more than two-thirds water, the balance being chiefly starch, with a little albumen.
28. Sweet potato? Nightshades? Potatoes when germinating?
28. The sweet potato differs from the white or common, in containing more water and a small proportion of sugar. The common potato and the tomato belong to the same botanical order as the "nightshades," but do not possess their poisonous qualities, unless we except potatoes that are in the process of germination or sprouting, when they are found injurious as food.
29. Fruits? Use of ripe fruit? Nutriment they contain? Starch in unripe fruits? Cooking of unripe fruits?
29. Fruits.—These are produced, in this country, in great abundance, and are remarkable alike for their variety and delicious flavor; consequently they are consumed in large quantities, especially during the warmer months. The moderate use of ripe fruits, in their season, is beneficial, because they offer a pleasant substitute for the more concentrated diet that is used in cold weather. The amount of solid nutriment they contain is, however, small. The percentage of water in cherries is seventy-five, in grapes eighty-one, in apples eighty-two. Unripe fruits contain starch, which, during the process of ripening, is converted into sugar. Such fruits are indigestible and should be avoided: cooking, however, in part removes the objections to them.
30. How should drinking-water be as regards color and smell? Chemically pure water? How obtained? Agreeableness of perfectly pure water?
30. Pure Water.—It is important that the water we drink and use in the preparation of food should be pure. It should be clear and colorless, with little or no taste or smell, and free from any great amount of foreign ingredients. Chemically pure water does not occur in nature: it is only obtained by the condensation of steam, carefully conducted, and is not as agreeable for drinking purposes as the water furnished by springs and streams. Rain-water is the purest occurring in nature; but even this contains certain impurities, especially the portion which falls in the early part of a shower; for in its descent from the clouds, the particles floating in the air are caught by the falling drops.
31. Spring and well water? Whence the sparkle, or life? The water supply of cities? Croton water? Ridgewood?
31. Water from springs and wells always contains more or less foreign matter of mineral origin. This imparts to the drink its pleasant taste—the sparkle, or "life," coming from the gases absorbed by the water during its passage under ground. The ordinary supply of cities is from some pure stream or pond conveyed from a distance through pipes, the limpid fluid containing generally only a small amount of impurity. Croton water, the supply of New York City, is very pure, and contains only four and a half grains to a gallon: the Ridgewood water of Brooklyn holds even less foreign matter.
32. Impurities in drinking-water? Mineral springs?
32. Drinking-water may contain as large a proportion as sixty to seventy grains per gallon of impurity, but a much larger quantity renders it unwholesome. The mineral spring waters, used popularly as medicines, are highly charged with mineral substances. Some of them, such as the waters at Saratoga, contain three hundred grains and more to the gallon.
33. What is stated of the action of water upon lead?
33. Action of Water upon Lead.—The danger of using water that has been in contact with certain metals is well known. Lead is one of the most readily soluble, and probably the most poisonous of these substances in common use. When pure water and an untarnished surface of lead come in contact, the water gradually corrodes the metal, and soon holds an appreciable quantity of it in solution. When this takes place the water becomes highly injurious: the purer the water, and the more recent the use of the metal, the greater will be the danger.
34. Lead in pipes and other things? Advice? What takes place after the articles of lead have been used much? What is wise?
34. In cities, lead pipes are commonly used to convey water through the houses; lead being also used in the construction of roofs, cisterns, and vessels for keeping water and other liquids. After the articles of lead have been in use several months, the danger of lead-poisoning diminishes. An insoluble coating of the sulphate of lead forms upon the exposed surface, thus protecting it from further corrosion. It is, however, a wise precaution, at all times to reject the water or other fluid that has been in contact with leaden vessels over night, or for a number of hours. Allow the water in pipes to run freely before using.
35. Coffee as an article of diet? Of what does it consist? How does the water affect the coffee? The peculiar stimulant? How does it affect most persons?
35. Coffee.—This is an important addition to diet, and if moderately used is beneficial to persons of adult age. As commonly employed, it consists of an infusion in boiling water of the roasted and ground berry. The water extracts certain flavoring and coloring matters, but that which gives it its peculiar stimulant qualities is the alkaloid caffein. With most persons its action is that of a gentle stimulant, without any injurious reaction. It produces a restful feeling after exhausting efforts of mind or body; it tranquilizes, but does not disqualify for labor; and hence it is highly esteemed by persons of literary pursuits.
36. Another property of coffee? Miners of Belgium? The Caravans? Among armies? Taken with meals?
36. Another property of coffee is, that it diminishes the waste of the tissues, and consequently permits the performance of excessive labor upon an economical and inadequate diet. This has been tested among the miners of Belgium. Their allowance of solid food was below that found necessary in prisons and elsewhere; but, with the addition of about four pints of coffee daily, they were enabled to undergo severe labor without reducing their muscular strength. The caravans which traverse the deserts are supported by coffee during long journeys and lengthened privation of food. Among armies it is indispensable in supplementing their imperfect rations, and in relieving the sense of fatigue after great exposure and long marches. When taken with meals, coffee is also thought to promote digestion.
37. Effects of tea-drinking? Peculiar principle? The tea beverage, how made? Black and green tea? Excessive use of tea or coffee?
37. Tea.—The effects of tea-drinking are very similar to those of coffee, and are due to a peculiar principle called thein. This principle is probably the same as that found in coffee, caffein, since the chemical composition of both is precisely alike. Tea, as a beverage, is made from the dried leaves of the plant by the addition of hot water; if the tea is boiled, the oil which gives it its agreeable flavor is driven off with the steam. There are two kinds of tea—the black and the green: the latter is sometimes injurious, producing wakefulness and other nervous symptoms. The excessive use of either coffee or tea will cause wakefulness.
38. Experiments made during Kane's expedition?
38. During Dr. Kane's expedition in the Arctic regions, the effects of these articles were compared. "After repeated trials, the men took most kindly to coffee in the morning and tea in the evening. The coffee seemed to continue its influence throughout the day, and they seemed to grow hungry less rapidly than after drinking tea, while tea soothed them after a day's hard labor, and the better enabled them to sleep. They both operated upon fatigued men like a charm, and their superiority over alcoholic stimulants was very decided."
39. State what is said of chocolate.
39. Chocolate is made from the seeds of the cocoa-tree, a native of tropical America. Its effects resemble somewhat those of tea and coffee, but it is very rich in nutriment. Linnæus, the botanist, was so fond of this beverage, that he gave to the cocoa-tree the name, Theobroma—"the Food of the Gods." Its active principle is theobromin.
40. Use of alcoholic drinks, how general? The rule given?
40. Alcohol.—The list of beverages that are consumed for the sake of the alcohol they contain is a very long one. Their use is almost universally prevalent, every civilized nation, and nearly every barbarous one, having its favorite alcoholic drink; and, as a general rule, the nations which stand the highest in civilization have the greatest varieties of these beverages,—at the same time using them the most intelligently and wisely.
41. The beverages produced by fermentation? The ardent spirits? Grains and fruits employed? Long use of wine? Of distilled liquors?
41. The wines and malt liquors that contain a small amount of alcohol are produced by fermentation. The beverages that hold a large proportion of alcohol, the "ardent spirits," are made by distillation. Enormous quantities of grains and fruits are thus yearly diverted from their proper uses as food; some of these being corn, wheat, rye, barley, potatoes, and rice; also the grape, apple, pear, peach, sugar-cane, cherry, fig, and orange. Wine, the fermented juice of the grape, has been in use from time immemorial, while the introduction of distilled liquors dates from a comparatively recent period.
42. Describe the action of alcohol upon the human system? Experience of Dr. Hayes and others?
42. What is the physiological action of alcohol? Its first and most evident action is stimulation: this effect is transient, and is followed by a variable degree of depression. At first it sharpens the appetite and quickens digestion, but its habitual use impairs both. This stimulation is efficient in giving the system an artificial strength during some temporary derangement, and in enabling the endurance of unusual fatigue or exposure. The experience of Dr. Hayes, and other explorers of the polar regions, is that alcohol does not enable the body to resist the influence of cold, but, on the contrary, is always injurious.
43. Another property of alcohol? How do we explain the restorative influence of wines and liquors?
43. Another property it has in common with tea and coffee. It supports the powers of life, economizes food, and retards the waste of tissues; in other words, it "banks the fires," and prevents their burning wastefully. On this principle we explain the restorative influence of wines or liquors during exhausting diseases, in convalescence, and after excessive labors of mind or body.
44. Alcohol, a poison? Moderate stimulants? Prevailing opinion? Hence?
44. Pure alcohol, or an excessive quantity of ardent spirits, is an undoubted poison, and has been frequently known to produce fatal results. Stimulants in moderate quantities have been thought to increase strength, and in this view they have been called "alcoholic foods." This is not now conceded by scientific men. The prevailing opinion is, that they serve no useful purpose as an article of diet, and that their beneficial influence is limited to cases where the system is enfeebled, where some unnatural demand is made upon the vital powers, or where the supply of food is insufficient. Hence, while alcohol has not the power to build up, it may obstruct the process of pulling down.
QUESTIONS FOR TOPICAL REVIEW.
PAGE 1. How is the necessity for food shown? [64] 2. To what process of waste and repair is the body constantly subjected? [64] 3. How do you account for the sensations of hunger and thirst? [65] 4. What further can you state having relation to the subject? [65] 5. What can you state in regard to the quantity of food required for the support of life? [65], [66] 6. What circumstances change the needs of persons, old and young, as regards food and drink? [65], [67] 7. What becomes of all the food and drink we consume? [66] 8. What further can you state in relation to the process of renovation through which the body passes? [66] 9. What can you state of the habits of nations in respect to diet? [66], [67], [69] 10. What in relation to the selection of articles for food? [67] 11. What as respects the necessity for changing or varying the diet? [67] 12. What has been proved as regards animal food? [67] 13. Of what importance is milk as an article of food? [67], [68] 14. What are the constituents of milk? [68] 15. What can you state of eggs as an article of food? [68] 16. Of the meats, so called, as an article of food? [68], [69] 17. What effect does cold have upon meats? [69] 18. In what other way may beef and pork be preserved? [69] 19. What can you state of salted meat as food, and of its continued use? [69] 20. What change does meat undergo in the cooking? [70], [71] 21. What directions are given for boiling meat? [70] 22. What for roasting, and with what results? [70], [71] 23. What is said about the frying of meats? [71] 24. Give the statement in relation to trichina. [71] 25. State what is said in relation to fish. [71] 26. What is stated of the usefulness and other properties of the products of the vegetable kingdom? [71], [72] 27. What further is said of vegetable food? [71], [72] 28. Why is bread made of wheat flour so important as an article of food? [72] 29. State whatever else you can in relation to bread. [72], [73] 30. Give the statement respecting the potato. [73] 31. What is stated of fruits, the use of them, their nutritious qualities, etc.? [73], [74] 32. How general is the existence of perfectly pure water? [74] 33. What is stated in relation to drinking water? [74], [75] 34. How does the action of water upon lead affect lead? [75] 35. What further can you state on the subject? [75] 36. What properties has coffee as an article of diet? [75], [76] 37. In what circumstances has coffee been found peculiarly beneficial? [76] 38. What comparison is made between coffee, tea, and chocolate? [76] 39. How are the wines, and malt and other alcoholic beverages produced? [77] 40. What articles are employed in their production? [77] 41. Describe the physiological action of alcohol. [78] 42. What comparison is made between tea, coffee, and alcohol? [78] 43. What can you state of alcohol, as a poison, a stimulant, and article of diet? [78] 44. What, then, can be said of alcohol as a recommendation? [78]
CHAPTER VI.
DIGESTION.
The Principal Processes of Nutrition—The General Plan of Digestion—Mastication—The Teeth—Preservation of the Teeth—Insalivation—The Stomach and the Gastric Juice—The Movements of the Stomach—Gastric Digestion—The Intestines—The Bile and Pancreatic Juice—Intestinal Digestion—Absorption by means of Blood-vessels and Lacteals—The Lymphatic or Absorbent System—The Lymph—Conditions which affect Digestion—The Quality, Quantity, and Temperature of the Food—The Influence of Exercise and Sleep.
1. Design of food? How accomplished?
1. Nutrition.—The great design of food is to give nutriment or nourishment to the body. But this is not accomplished directly, as the food must first pass through certain preparatory changes, as follows: (1), Digestion, by which the food is reduced to a soluble condition; (2), Absorption, by which, when digested, it is imbibed into the blood; (3), Circulation, which carries the enriched blood to the various parts of the system; and (4), Assimilation, by which each tissue derives from the blood the materials necessary for its support.
2. Sustaining power of food? Simile of the engine? Operation in the human body?
2. By these means the sustaining power of food is gradually developed and employed, and the vital machinery kept in working order, somewhat after the manner of the steam-engine. To operate the latter, the force imprisoned within the coal and water is set free and converted into motion by the combustion of the fuel and the vaporization of the water. It will be seen, however, when we come to study these operations in the human body, that they are conducted silently and harmoniously, with marvellous delicacy and completeness, and without that friction, and consequent loss of power, which attend the working of the most perfect machinery of man's invention.
3. Change of food in digestion? Process of digestion? Describe the alimentary canal.
3. General Plan of Digestion.—The great change which food undergoes in digestion is essentially a reforming process, reducing articles of diet, which are at first more or less solid, crude, and coarse, to a liquid and finely comminuted condition, suitable for absorption into the blood. The entire process of digestion takes place in what is called the alimentary canal, a narrow, tortuous tube, about thirty feet in its entire length. This canal begins in the mouth, extends thence downward through the gullet to the stomach (a receptacle in which the principal work of digestion is performed), and thence onward through the small and large intestines.
Fig. 16.—Section of the Trunk Showing the Cavities of the Chest and Abdomen.
A, Cavity of Chest; B, Diaphragm; C, Abdomen; D, E, Spinal Column.
4. Situation of the stomach and intestines? Action of the food? Mechanical action? Chemical?
4. The stomach and intestines are situated in the cavity of the abdomen (Fig. 16, C, and Fig. 22), and occupy about two-thirds of its space. The action to which the food is subjected in these organs is of two kinds—mechanical and chemical. By the former it is crushed, agitated, and carried onward from one point to another; by the latter it is changed in form through the solvent power of the various digestive juices.
5. Describe the process of mastication? How many and what movements?
5. Mastication.—As soon as solid food is taken into the mouth, it undergoes mastication, or chewing. It is caught between the opposite surfaces of the teeth, and by them is cut and crushed into very small fragments. In the movements of chewing, the lower jaw plays the chief part; the upper jaw, having almost no motion, acts simply as a point of resistance, to meet the action of the former. These movements of the lower jaw are of three sorts: a vertical or cutting, a lateral or grinding, and a to-and-fro or gnawing motion.
Fig. 17.—Section of a Tooth.
a, Enamel; b, Cavity; c c, Roots; d, Body of the Tooth.
6. Composition of the teeth? Enamel of the teeth? Interior of teeth?
6. The teeth are composed of a bone-like material, and are held in place by roots running deeply into the jaw. The exposed portion, or "crown," is protected by a thin layer of enamel (Fig. 17, a), the hardest substance in the body, and, like flint, is capable of striking fire with steel. In the interior of each tooth is a cavity, containing blood-vessels and a nerve, which enter it through a minute opening at the point of the root (Fig. 19).
7. The milk teeth? The permanent teeth?
7. There are two sets of teeth; first, those belonging to the earlier years of childhood, called the milk teeth, which are twenty in number and small. At six or eight years of age, when the jaw expands, and when the growing body requires a more powerful and numerous set, the roots of the milk teeth are absorbed, and the latter are "shed," or fall out, one after another (Fig. 18), to make room for the permanent set.
Fig. 18.—Section of the Jaws.
1' 2' 3' 4' 5', The Milk Teeth; 1" to 8", The Germs of the Permanent Set.
8, 9. Number of teeth? How distributed?
8. There are thirty-two teeth in the permanent set, as many being in one jaw as the other. Each half-jaw has eight teeth, similarly shaped and arranged in the same order: thus, two incisors, one canine, two bicuspids, and three molars. The front teeth are small, sharp, and chisel-edged, and are well adapted for cutting purposes; hence their name incisors. The canines stand next, one on each side of the jaw; these receive their name from their resemblance to the long, pointed tusks of the dog (Fig. 19).
Fig. 19.—Section of the Jaws—Right Side.
V, A, N, Veins, Arteries, and Nerves of the Teeth. The root of one tooth in each jaw is cut vertically to show the cavity and the blood-vessels, etc., within it. 1 to 8, Permanent Teeth.
9. The bicuspids, next in order, are larger and have a broader crown than the former; while behind them are the molars, the largest and most powerful of the entire set. These large back teeth, or "grinders," present a broad, rough surface, suitable for holding and crushing the food. The third molar, or "wisdom tooth," is the last to be cut, and does not appear until about the twenty-first year. The order of arrangement of the teeth is indicated by the following dental formula:—
10. Different forms of teeth? Human teeth? The inference?
10. It is interesting, at this point, to notice the different forms of teeth in different animals, and observe how admirably their teeth are suited to the respective kinds of food upon which they subsist. In the carnivora, or flesh-feeders, the teeth are sharp and pointed, enabling them both to seize their prey, and tear it in pieces; while the herbivora, or vegetable-feeders, have broad, blunt teeth, with rough crowns, suitable for grinding the tough grasses and grains upon which they feed. Human teeth partake of both forms; some of them are sharp, and others are blunt; they are therefore well adapted for the mastication of both flesh and vegetables. Hence we argue that, although man may live exclusively upon either vegetable or animal food, he should, when possible, choose a diet made up of both varieties.
11. Cleaning of teeth? Effects of not cleaning?
11. Preservation of the Teeth.—In order that the teeth shall remain in a sound and serviceable condition, some care is of course requisite. In the first place, they require frequent cleansing; for every time we take food, some particles of it remain in the mouth; and these, on account of the heat and moisture present, soon begin to putrefy. This not only renders the breath very offensive, but promotes decay of the teeth.
12. Effects upon the saliva? Formation of tartar? How prevented? How destroyed?
12. The saliva, or moisture of the mouth, undergoes a putrefactive change, and becomes the fertile soil in which a certain minute fungus has its growth. This fluid, too, if allowed to dry in the mouth, collects upon the teeth in the form of an unsightly, yellow concretion, called tartar. To prevent this formation, and to remove other offensive substances, the teeth should be frequently cleaned with water, applied by means of a soft tooth-brush. The destruction of the tartar fungus is best effected by the use of a weak solution of carbolic acid.
13. Destruction of the enamel? How guarded against?
13. Again, it should be borne in mind that the enamel, Nature's protection for the teeth, when once destroyed, is not formed anew; and the body of the tooth thus exposed, is liable to rapid decay. On this account, certain articles are to be guarded against; such as sharply acid substances that corrode the enamel, and hard substances that break or scratch it—as gritty tooth powders, metal tooth picks, and the shells of hard nuts. Sudden alternations from heat to cold, when eating or drinking, also tend to crack the enamel.
14. Mixing of food with the saliva? What is the saliva? How secreted? The salivary glands?
14. Insalivation.—When the morsel of food is cut and ground by the teeth, it is at the same time also intimately mixed with the saliva, or fluids of the mouth. This constitutes the second step of digestion, and is called insalivation. The saliva, the first of the digestive solvents, is a colorless, watery, and frothy fluid. It is secreted (i. e. separated from the blood) partly by the mucous membrane which lines the mouth; but chiefly by the salivary glands, of which there are three pairs situated near the mouth.
15. The flow of saliva? The thought of food? Anxiety and grief? Animals fed upon dry and coarse food?
15. These glands consist of clusters of very small pouches, around which a delicate network of blood-vessels is arranged: they empty into the mouth by means of little tubes, or ducts. The flow from these glands is at all times sufficient to maintain a soft and moist condition of the tongue and mouth; but when they are excited by the presence and taste of food, they pour forth the saliva more freely. Even the mere thought of food will at times cause the saliva to flow, as when the appetite is stimulated by the sight or smell of some savory article; so that the common expression is correct that "the mouth waters" for the favorite articles of food. Anxiety and grief prevent its flow, and cause "the tongue to cleave to the roof of the mouth." In the horse and other animals, that feed upon dry and coarse fodder, and require an abundant supply of saliva, we find large salivary glands, as well as powerful muscles of mastication.
| PAGE | |
| 1. How is the necessity for food shown? | [64] |
| 2. To what process of waste and repair is the body constantly subjected? | [64] |
| 3. How do you account for the sensations of hunger and thirst? | [65] |
| 4. What further can you state having relation to the subject? | [65] |
| 5. What can you state in regard to the quantity of food required for the support of life? | [65], [66] |
| 6. What circumstances change the needs of persons, old and young, as regards food and drink? | [65], [67] |
| 7. What becomes of all the food and drink we consume? | [66] |
| 8. What further can you state in relation to the process of renovation through which the body passes? | [66] |
| 9. What can you state of the habits of nations in respect to diet? | [66], [67], [69] |
| 10. What in relation to the selection of articles for food? | [67] |
| 11. What as respects the necessity for changing or varying the diet? | [67] |
| 12. What has been proved as regards animal food? | [67] |
| 13. Of what importance is milk as an article of food? | [67], [68] |
| 14. What are the constituents of milk? | [68] |
| 15. What can you state of eggs as an article of food? | [68] |
| 16. Of the meats, so called, as an article of food? | [68], [69] |
| 17. What effect does cold have upon meats? | [69] |
| 18. In what other way may beef and pork be preserved? | [69] |
| 19. What can you state of salted meat as food, and of its continued use? | [69] |
| 20. What change does meat undergo in the cooking? | [70], [71] |
| 21. What directions are given for boiling meat? | [70] |
| 22. What for roasting, and with what results? | [70], [71] |
| 23. What is said about the frying of meats? | [71] |
| 24. Give the statement in relation to trichina. | [71] |
| 25. State what is said in relation to fish. | [71] |
| 26. What is stated of the usefulness and other properties of the products of the vegetable kingdom? | [71], [72] |
| 27. What further is said of vegetable food? | [71], [72] |
| 28. Why is bread made of wheat flour so important as an article of food? | [72] |
| 29. State whatever else you can in relation to bread. | [72], [73] |
| 30. Give the statement respecting the potato. | [73] |
| 31. What is stated of fruits, the use of them, their nutritious qualities, etc.? | [73], [74] |
| 32. How general is the existence of perfectly pure water? | [74] |
| 33. What is stated in relation to drinking water? | [74], [75] |
| 34. How does the action of water upon lead affect lead? | [75] |
| 35. What further can you state on the subject? | [75] |
| 36. What properties has coffee as an article of diet? | [75], [76] |
| 37. In what circumstances has coffee been found peculiarly beneficial? | [76] |
| 38. What comparison is made between coffee, tea, and chocolate? | [76] |
| 39. How are the wines, and malt and other alcoholic beverages produced? | [77] |
| 40. What articles are employed in their production? | [77] |
| 41. Describe the physiological action of alcohol. | [78] |
| 42. What comparison is made between tea, coffee, and alcohol? | [78] |
| 43. What can you state of alcohol, as a poison, a stimulant, and article of diet? | [78] |
| 44. What, then, can be said of alcohol as a recommendation? | [78] |
Fig. 20.—Structure of a Salivary Gland.
Fig. 21.—The Head of a Horse, showing the large salivary gland (a), its duct (b), the muscles of mastication (c, d, e, f, and g).
16. Importance of the process? The first place? The second? The third?
16. The mingling of the saliva with the food seems a simple process, but it is one that plays an important part in digestion. In the first place, it facilitates the motions of mastication, by moistening the food and lubricating the various organs of the mouth. Secondly, it prepares the way for other digestive acts: by the action of the teeth, the saliva is forced into the solid food, softens the harder substances, and assists in converting the whole morsel into a semi-solid, pulpy mass, that can be easily swallowed, and readily permeated by other digestive fluids. The saliva also, by dissolving certain substances, as sugar and salt, develops the peculiar taste of each; whereas, if the tongue be dry and coated, they are tasteless. Hence, if substances are insoluble, they are devoid of taste.
17. Its final importance? Starch? How effected? Ptyalin?
17. Finally, the saliva has the property of acting chemically upon the food. As we have before stated (Chap. IV.), starch, as starch, cannot enter the tissues of the body; but, in order to become nutriment, must first be changed to grape sugar. This change is, in part, effected by the saliva, and takes place almost instantly, whenever it comes in contact with cooked starch. This important function is due to an organic ingredient of the saliva called ptyalin. This substance has been extracted from the saliva by the chemist, and has been found, by experiment, to convert into sugar two thousand times its own weight of starch.
18. Each of the processes? Why is a knowledge of the digestive functions important? How shown?
18. Importance of Mastication and Insalivation.—Each of these processes complements the other, and makes the entire work available; for, by their joint action, they prepare the food in the best possible manner for further digestive changes. The knowledge of these preliminary functions will appear the more important, when we reflect that they are the only ones which we can regulate by the will. For, as soon as the act of swallowing begins, the food not only passes out of sight, but beyond control; and the subsequent acts of digestion are consequently involuntary and unconsciously performed.
19. Rapid eating? Describe the process and effects.
19. It is generally known that rapid eating interferes with digestion. How does this occur? In the first place, in rapid eating, the flow of the saliva is insufficient to moisten the solid parts of the food, so that they remain too hard and dry to be easily swallowed. This leads to the free and frequent use of water, or some other beverage, at meals, to "wash down" the food,—a most pernicious practice. For these fluids, not only cannot take the place of the natural digestive juices, but, on the contrary, dilute and weaken them.
20. Loss of taste? Another effect of rapid eating? Mistakes?
20. Secondly, the saliva being largely the medium of the sense of taste, the natural flavors of the food are not developed, and consequently it appears comparatively insipid. Hence the desire for high-seasoned food, and pungent sauces, that both deprave the taste and over excite the digestive organs. Rapid eating also permits the entrance of injurious substances which may escape detection by the taste, and be unconsciously received into the system. In some instances, the most acrid and poisonous substances have frequently been swallowed "by mistake," before the sense of taste could act, and demand their rejection.
21. Effect of imperfectly broken food in the stomach? Dyspepsia? Overeating?
21. Thirdly, the food, being imperfectly broken up by the teeth, is hurried onward to the stomach, to be by it more thoroughly divided. But the task thus imposed upon the stomach, it is not at all adapted to perform; so that the crude masses of food remain a heavy burden within the stomach, and a source of distress to that organ, retarding the performance of its legitimate duty. Hence persons who habitually eat too rapidly, frequently fall victims to dyspepsia. Rapid eating also conduces to overeating. The food is introduced so rapidly, that the system has not time to recognize that its real wants are met, and that its losses have been made good; and hence the appetite continues, although more nutriment has been swallowed than the system requires, or can healthfully appropriate.
Fig. 22.—Section of Chest and Abdomen.
A, Heart. B, The Lungs. C, Stomach. D, The Liver. E, Large Intestine. G, Small Intestine.
22. Gullet? Describe the stomach and its location. Effects of gormandizing?
22. The Stomach.—As soon as each separate portion of food is masticated and insalivated, it is swallowed; that is, it is propelled downward to the stomach, through a narrow muscular tube about nine inches in length, called the œsophagus, or gullet (Fig. 23). The stomach is the only large expansion of the digestive canal, and is the most important organ of digestion. It is a hollow, pear-shaped pouch, having a capacity of three pints, in the adult. Its walls are thin and yielding, and may become unnaturally distended, as in the case of those who subsist on a bulky, innutritious diet, and of those who habitually gormandize.
23. Heart-orifice? Gatekeeper? Coins, etc.? Indication of the soft and yielding texture of the stomach?
23. The stomach has also two openings; that by which food enters, being situated near the heart, is called the cardiac, or heart orifice; the other is the pylorus, or "gatekeeper," which guards the entrance to the intestines, and, under ordinary circumstances, permits only such matters to pass it as have first been properly acted upon in the stomach. Coins, buttons, and the like are, however, readily allowed to pass, because they can be of no use if retained. The soft and yielding texture of this organ—the stomach—indicates that it is not designed to crush and comminute solid articles of food.
Fig. 23.—The Organs of Digestion.
O, Œsophagus. S, Stomach. L, Liver. M, Pylorus. C, Large Intestines. P, Pancreas. I, Small Intestines. N, Spleen. G, Gall-bladder.
24. What is meant by the gastric juice?
24. The Gastric Juice.—We have seen how the presence of food in the mouth excites the salivary glands, causing the saliva quickly to flow. In the same manner, when food reaches the stomach, its inner lining, the mucous membrane, is at once excited to activity. (At first its surface, which while the stomach is empty presents a pale pink hue, turns to a bright red color, for the minute blood-vessels which course through it, are filled with blood. Presently a clear, colorless, and acid fluid exudes, drop by drop, from its numerous minute glands or "tubules," until finally the surface is moistened in every part, and the fluid begins to mingle with the food. This fluid is termed the gastric juice.
25. What is the office of the gastric juice? Acidity of the gastric juice? Quantity of gastric juice used? What becomes of it?
25. The gastric juice is the proper solvent of certain articles of food, especially those belonging to the albuminoid class. This solvent power is due to its peculiar ingredient, pepsin; in digestion, this substance acts like a ferment; that is, it induces changes in the food simply by its presence, but does not itself undergo change. The acidity of the gastric juice, which is due to lactic acid, is not accidental; for we find that the pepsin cannot act in an alkaline solution—that is, one which is not acid or neutral. The quantity of gastric juice secreted daily is very large, probably not less than three or four pints at each meal. Though this fluid is at once used in the reduction of the food, it is not lost; since it is soon re-absorbed by the stomach, together with those parts of the food which it has digested and holds in solution.
26. Muscular coat of the stomach? Expansion and contraction of its fibres? Action of the fibres?
26. Movements of the Stomach.—The inner coating of the stomach is the mucous membrane, which, as we have seen, furnishes the gastric juice. Next to this coating lies another, called the muscular coat, composed of involuntary muscular fibres, some of which run circularly, and others in a longitudinal direction. These expand to accommodate the food as it is introduced, and contract as it passes out. In addition, these fibres are in continual motion while food remains in the stomach, and they act in such manner that the contents are gently turned round from side to side, or from one end of it to the other.
27. Peristaltic movements? What is said of our consciousness of and power over these movements? Describe the movements of the pylorus.
27. By these incessant movements of the stomach, called the peristaltic movements, the gastric juice comes in contact with all parts of the food. We are, however, not conscious that these movements take place, nor have we the power to control them. When such portions of the food as are sufficiently digested approach the pylorus, it expands to allow them to pass out, and it closes again to confine the residue for further preparation.
28. How has the knowledge and the workings of the stomach been ascertained? St. Martin? How else?
28. The knowledge of these and other interesting and instructive facts has been obtained by actual observation; the workings of the stomach of a living human being have been laid open to view and examined—the result of a remarkable accident. Alexis St. Martin, a Canadian voyageur, received a gun-shot wound which laid open his stomach, and which, in healing, left a permanent orifice nearly an inch in diameter. Through this opening the observer could watch the progress of digestion, and experiment with different articles of food. Since that occurrence, artificial openings into the stomach of the inferior animals have been repeatedly made, so that the facts of stomach-digestion are very well ascertained and verified.
29. What was formerly thought? What do we now know? What else do we now know? Water, salt, and sugar? Absorption?
29. Gastric Digestion.—What portions of the food are digested in the stomach? It was formerly thought that all the great changes of digestion were wrought here, but later investigation has taught us better. We now know that the first change in digestion takes place in the mouth, in the partial conversion of starch into sugar. We also know that, of the three organic food principles (considered in Chapter IV.) two—the fats and the sugars—are but slightly affected by the stomach; but that its action is confined to that third and very important class, from which the tissues are renewed, the albuminoids. A few articles need no preparation before entering the system, as water, salt, and grape-sugar. These are rapidly taken up by the blood-vessels of the stomach, which everywhere underlie its mucous membrane in an intricate and most delicate network. In this way the function of absorption begins.
30. Albuminose? The process? Chyme?
30. The albuminoid substances are speedily attacked and digested by the gastric juice. From whatever source they are derived, vegetable or animal, they are all transformed into the same digestive product, called albuminose. This is very soluble in water, and is readily absorbed by the blood-vessels of the stomach. After a longer or shorter time, varying from one to five hours, according to the individual and the quantity and quality of his food, the stomach will be found empty. Not only has the digested food passed out, but also those substances which the stomach could not digest or absorb have passed little by little through the pylorus, to undergo further action in the intestines. At the time of its exit, the digested food is of a pulpy consistence, and dark color, and is then known as the chyme.
31. What are the intestines? The small intestines? The large intestines? Their structure?
31. The Intestines.—The intestines, or "bowels," are continuous with the stomach, and consist of a fleshy tube, or canal, twenty-five feet in length. The small intestine, whose diameter is about one inch and a half, is twenty feet long and very tortuous. The large intestine is much wider than the former, and five feet long (Fig. 23). The general structure of these organs resembles that of the stomach. Like it, they are provided with a mucous membrane, or inner lining, whence flow their digestive juices; and, just outside of this, a muscular coat, which propels the food onward from one point to another.
32. Peritoneum? The work of digestion?
32. Moreover, both the intestines and stomach are enveloped in the folds of the same outer tunic or membrane, called the peritoneum. This is so smooth and so well lubricated, that the intestines have the utmost freedom of motion. In the small intestines, the work of digestion is completed, the large intestine receiving from them the indigestible residue of the food, and in time expelling it from the body.
33. The presence of food in the intestines? Bile?
33. Intestinal Digestion.—As soon as the food passes the pylorus and begins to accumulate in the upper part of the intestines, it excites the flow of a new digestive fluid, which enters through a small tube, or duct, about three inches below the stomach. It is formed by the union of two distinct fluids—the bile and the pancreatic juice. The bile is secreted by the liver, which is the largest gland of the body, and is situated on the right side and upper part of the abdomen (Fig. 22). The bile is constantly formed, but it flows most rapidly during digestion. During the intervals of digestion it is stored in the gall-bladder, a small membranous bag attached to the under side of the liver. This fluid is of a greenish-yellow color, having a peculiar smell, and a very bitter taste.
34. The pancreatic juice? The joint action of these fluids?
34. The pancreatic juice is the product of a gland called the pancreas, situated behind the stomach. This fluid is colorless, viscid, and without odor. Like the digestive juices previously described, it owes its solvent power to its peculiar ferment principle, called pancreatin. By the joint action of these fluids, the fatty parts of the food are prepared for absorption. By previous steps of digestion the fats are merely separated from the other components of the food; but here, within the intestines, they are reduced to a state of minute division, or emulsion, resembling the condition of butter in milk, before it has been churned. There results from this action a white and milky fluid, termed the chyle, which holds in solution the digestible portions of the food, and is spread over the extensive absorbent surface of the small intestines.
35. The mucous membrane? Experiments on inferior animals?
35. The mucous membrane of the intestines, also, secretes or produces, a digestive fluid by means of numerous "follicles," or minute glands; this is called the intestinal juice. From experiments on the inferior animals, it has been ascertained that this fluid exerts a solvent influence over each of the three organic food principles, and in this way may supplement and complete the action of the fluids previously mentioned, viz.:—of the saliva in converting starch into sugar, of the gastric juice in digesting the albuminoids, and of the pancreatic juice and bile in emulsifying the fats.
36, 37. How much thus far has been done with the food? The next process? Give the first way.
36. Absorption.—With the elaboration of the chyle, the work of digestion is completed; but, in a certain sense, the food is yet outside of the body; that is, the blood is not yet enriched by it, and it is not in a position to nourish the tissues. The process by which the liquefied food passes out of the alimentary canal into the blood is called absorption. This is accomplished in two ways; first, by the blood-vessels. We have seen how the inner membrane of the stomach is underlaid by a tracery of minute and numerous vessels, and how some portions of the food are by them absorbed. The supply of blood-vessels to the intestines is even greater; particularly to the small intestines, where the work of absorption is more actively carried on.
37. The absorbing surface of the small intestines, if considered as a plane surface, amounts to not less than half a square yard. Besides, the mucous membrane is formed in folds with an immense number of thread-like prolongations, called villi, which indefinitely multiply its absorbing capacity. These minute processes, the villi, give the surface the appearance and smoothness of velvet; and during digestion, they dip into the canal, and, by means of their blood-vessels, absorb its fluid contents, just as the spongioles which terminate the rootlets of plants, imbibe moisture from the surrounding soil.
38. How is absorption effected in another way? Describe it. Name of the lacteals? Thoracic duct?
38. Secondly, absorption is also effected by the lacteals, a set of vessels peculiar to the small intestines. These have their beginnings in the little villi just mentioned, side by side with the blood-vessels. These two sets of absorbents run in different courses, but their destination is the same, which is the right side of the heart. The lacteals receive their name from their milky-white appearance. After a meal containing a portion of fat, they are then distended with chyle, which they are specially adapted to receive: at other times they are hardly discernible. The lacteals all unite to form one tube, the thoracic duct, which passes upward through the thorax, or chest, and empties into a large vein, situated just beneath the left collar-bone.
Fig. 24.—The Lacteals.
A, Small Intestine. B, Lacteals. C, Thoracic Duct. D, Absorbents. E, Blood-vessel.
39. The absorbents? Lymph? What further of the lymph?
39. The Absorbents.—The lacteals belong to a class of vessels known as absorbents, or lymphatics, which ramify in nearly all parts of the body, except the brain and spinal cord. The fluid which circulates through the lymphatics of the limbs, and all the organs not concerned in digestion, is called lymph. This fluid is clear and colorless, like water, and thus differs from the milky chyle which the lacteals carry after digestion: it consists chiefly of the watery part of the blood, which was not required by the tissues, and is returned to the blood by the absorbents or lymphatics.
40. What can you state as to the time required for digestion?
40. Circumstances affecting Digestion.—What length of time is required for the digestion of food? From observations made, in the case of St. Martin, the Canadian already referred to, it has been ascertained that, at the end of two hours after a meal, the stomach is ordinarily empty. How much time is needed to complete the digestion of food, within the small intestines, is not certain; but, from what we have learned respecting their functions, it must be evident that it largely depends upon the amount of starch and fat which the food contains.
41. Circumstances affecting duration of digestion? Fresh food?
41. In addition to the preparations which the food undergoes in cooking, which we have already considered, many circumstances affect the duration of digestion; such as the quality, quantity, and temperature of the food; the condition of the mind and body; sleep, exercise, and habit. Fresh food, except new bread and the flesh of animals recently slain, is more rapidly digested than that which is stale; and animal food more rapidly than that from the vegetable kingdom.
42. Food in concentrated form? A large quantity of food? Experiment on the dog? Ice-water? Variety of articles?
42. Food should not be taken in too concentrated a form, the action of the stomach being favored when it is somewhat bulky; but a large quantity in the stomach often retards digestion. If the white of one egg be given to a dog, it will be digested in an hour, but if the white of eight eggs be given it will not disappear in four hours. A wineglassful of ice-water causes the temperature of the stomach to fall thirty degrees; and it requires a half-hour before it will recover its natural warmth—about a hundred degrees—at which the operations of digestion are best conducted. A variety of articles, if not too large in amount, is more easily disposed of than a meal made of a single article; although a single indigestible article may interfere with the reduction of articles that are easily digested.
43. Strong emotion? The tongue of the patient?
43. Strong emotion, whether of excitement or depression, checks digestion, as do also a bad temper, anxiety, long fasting, and bodily fatigue. The majority of these conditions make the mouth dry, that is, they restrain the flow of the saliva; and without doubt they render the stomach dry also, by preventing the flow of the gastric juice. And, as a general rule, we may decide, from a parched and coated tongue, that the condition of the stomach is not very dissimilar, and that it is unfit for the performance of digestive labor. This is one of the points which the physician bears in mind when he examines the tongue of his patient.
44. Eating between meals? Severe exercise? Sleep after meals?
44. The practice of eating at short intervals, or "between meals," as it is called, has its disadvantage, as well as rapid eating and over-eating, since it robs the stomach of its needed period of entire rest, and thus overtasks its power. With the exception of infants and the sick, no persons require food more frequently than once in four hours. Severe exercise either directly before or directly after eating retards digestion; a period of repose is most favorable to the proper action of the stomach. The natural inclination to rest after a hearty meal may be indulged, but should not be carried to the extent of sleeping; since in that state the stomach, as well as the brain and the muscles, seeks release from labor.
QUESTIONS FOR TOPICAL REVIEW.
PAGE 1. What do you understand by nutrition? [80] 2. How is the process of nutrition carried on? [80] 3. What further can you state on the subject? [80], [81] 4. Describe the general plan of digestion. [81] 5. How is the process of mastication carried on? [80], [82] 6. State what you can in relation to the formation of the teeth. [82], [86] 7. What, in relation to their arrangement? [83], [84] 8. What, in relation to the process of "shedding?" [82], [83], [84] 9. In relation to the different forms of teeth in different animals? [85] 10. What causes operate to injure or destroy the teeth? [85], [86] 11. What suggestions and directions are given for the preservation of the teeth? [85], [86] 12. What do you understand by insalivation? [80], [86] 13. How is the process of insalivation carried on? [86], [87], [88] 14. Of what importance is the saliva to the process? [87], [88] 15. Of what importance are mastication and insalivation? [88], [89] 16. Describe the consequences of rapid eating. [89], [90] 17. What becomes of the food directly after it has undergone mastication and insalivation? [90] 18. Describe the location and formation of the stomach. [90], [91], [92] 19. Describe the process by which the gastric juice is formed. [91] 20. What are the properties and uses of the gastric juice? [92] 21. What are the movements of the stomach, and what their uses? [92], [93] 22. What further can you state on the subject? [93] 23. What portions of the food are digested in the stomach? [93], [94] 24. What are the first changes of digestion? [93] 25. Describe the location and formation of the stomach. [94] 26. What further can you state in relation to the stomach? [94] 27. Describe the process of intestinal digestion. [94], [95], [96] 28. What do you understand by absorption? [80], [96] 29. How is the process of absorption effected? [96], [97] 30. What are the lacteals and of what use are they? [96], [97] 31. What length of time is required for the digestion of food? [97], [98] 32. What circumstances, of food, affect digestion? [98] 33. What circumstances, of emotion, affect digestion? [98], [99] 34. What suggestions and directions are given upon the subject of eating and drinking? [98], [99]
CIRCULATION OF THE BLOOD.
[Heart, Lungs, Arteries & Veins.]
CHAPTER VII.
The Circulation.
The Blood—Its Plasma and Corpuscles—Coagulation of the Blood—The Uses of the Blood—Transfusion—Change of Color—The Organs of the Circulation—The Heart, Arteries, and Veins—The Cavities and Valves of the Heart—Its Vital Energy—Passage of the Blood through the Heart—The Frequency and Activity of its Movements—The Pulse—The Sphygmograph—The Capillary Blood-vessels—The Rate of the Circulation—Assimilation—Injuries to the Blood-vessels.
1. What is required by every living organism? In plants? Insects? Reptiles? Man?
1. The Blood.—Every living organism of the higher sort, whether animal or vegetable, requires for the maintenance of life and activity, a circulatory fluid, by which nutriment is distributed to all its parts. In plants, this fluid is the sap; in insects, it is a watery and colorless blood; in reptiles and fishes, it is red but cold blood; while in the nobler animals and man, it is the red and warm blood.
2. Importance and abundance of blood? Dependence of life? Abel? Mosaic law? In what part of the body is blood not found? Quantity of blood in the body?
2. The blood is the most important, as it is the most abundant, fluid of the body; and upon its presence, under certain definite conditions, life depends. On this account it is frequently, and very properly, termed "the vital fluid." The importance of the blood, as essential to life, was recognized in the earliest writings. In the narration of the death of the murdered Abel, it is written, "the voice of his blood crieth from the ground." In the Mosaic law, proclaimed over thirty centuries ago, the Israelites were forbidden to eat food that contained blood, for the reason that "the life of the flesh is in the blood." With the exception of a few tissues, such as the hair, the nails, and the cornea of the eye, blood everywhere pervades the body, as may be proven by puncturing any part with a needle. The total quantity of blood in the body is estimated at about one-eighth of its weight, or eighteen pounds.
3. Color of blood? Its consistence? Odor?
3. The color of the blood, in man and the higher animals, as is well known, is red; but it varies from a bright scarlet to a dark purple, according to the part whence it is taken. "Blood is thicker than water," as the adage truly states, and has a glutinous quality. It has a faint odor, resembling that peculiar to the animal from which it is taken.
4. What is stated of the blood as viewed under the microscope?
4. When examined under the microscope, the blood no longer appears a simple fluid, and its color is no longer red. It is then seen to be made up of two distinct parts: first, a clear, colorless fluid, called the plasma; and secondly, of a multitude of minute solid bodies, or corpuscles, that float in the watery plasma. The plasma, or nutritive liquid, is composed of water richly charged with materials derived from the food, viz., albumen, which gives it smoothness and swift motion; fibrin; certain fats; traces of sugar; and various salts.
Fig 25.—The Blood Corpuscles.
5. State what you can of the little bodies called corpuscles.
5. The Blood Corpuscles.—In man, these remarkable "little bodies," as the word corpuscles signifies, are of a yellow color, but by their vast numbers impart a red hue to the blood. They are very small, having a diameter of about 1/3500 of an inch, and being one-fourth of that fraction in thickness; so that if 3,500 of them were placed in line, side by side, they would only extend one inch; or, if piled one above another, it would take at least 14,000 of them to stand an inch high. Although so small in size, they are very regular in form. As seen under the microscope, they are not globular or spherical, but flat, circular, and disc-like, with central depressions on each side, somewhat like a pearl button that has not been perforated. In freshly-drawn blood they show a disposition to arrange themselves in little rolls like coins (Fig. 25).
Fig. 26.
a, Oval Corpuscles of a fowl. b, Corpuscles of a frog. c, Those of a shark.
The five small ones at the upper part of the figure, represent the human corpuscles magnified 400 times.
6. The size and shape of corpuscles? Why is the fact important?
6. The size and shape of the blood corpuscles vary in different animals, so that it is possible to discriminate between those of man and the lower animals (Fig. 26). This is a point of considerable practical importance. For example, it is sometimes desirable to decide in a court of justice the source, whether from man or an inferior animal, of blood stains upon the clothing of an accused person, or upon some deadly weapon. This may be done by a microscopical examination of a minute portion of the dried stain, previously refreshed by means of gum-water. Certain celebrated cases are recorded in which the guilt of criminals has been established, and they have been condemned and punished upon the evidence which science rendered on this single point, the detecting of the human from other blood.
| PAGE | |
| 1. What do you understand by nutrition? | [80] |
| 2. How is the process of nutrition carried on? | [80] |
| 3. What further can you state on the subject? | [80], [81] |
| 4. Describe the general plan of digestion. | [81] |
| 5. How is the process of mastication carried on? | [80], [82] |
| 6. State what you can in relation to the formation of the teeth. | [82], [86] |
| 7. What, in relation to their arrangement? | [83], [84] |
| 8. What, in relation to the process of "shedding?" | [82], [83], [84] |
| 9. In relation to the different forms of teeth in different animals? | [85] |
| 10. What causes operate to injure or destroy the teeth? | [85], [86] |
| 11. What suggestions and directions are given for the preservation of the teeth? | [85], [86] |
| 12. What do you understand by insalivation? | [80], [86] |
| 13. How is the process of insalivation carried on? | [86], [87], [88] |
| 14. Of what importance is the saliva to the process? | [87], [88] |
| 15. Of what importance are mastication and insalivation? | [88], [89] |
| 16. Describe the consequences of rapid eating. | [89], [90] |
| 17. What becomes of the food directly after it has undergone mastication and insalivation? | [90] |
| 18. Describe the location and formation of the stomach. | [90], [91], [92] |
| 19. Describe the process by which the gastric juice is formed. | [91] |
| 20. What are the properties and uses of the gastric juice? | [92] |
| 21. What are the movements of the stomach, and what their uses? | [92], [93] |
| 22. What further can you state on the subject? | [93] |
| 23. What portions of the food are digested in the stomach? | [93], [94] |
| 24. What are the first changes of digestion? | [93] |
| 25. Describe the location and formation of the stomach. | [94] |
| 26. What further can you state in relation to the stomach? | [94] |
| 27. Describe the process of intestinal digestion. | [94], [95], [96] |
| 28. What do you understand by absorption? | [80], [96] |
| 29. How is the process of absorption effected? | [96], [97] |
| 30. What are the lacteals and of what use are they? | [96], [97] |
| 31. What length of time is required for the digestion of food? | [97], [98] |
| 32. What circumstances, of food, affect digestion? | [98] |
| 33. What circumstances, of emotion, affect digestion? | [98], [99] |
| 34. What suggestions and directions are given upon the subject of eating and drinking? | [98], [99] |
7. The character of the blood of dead animals? Means of detecting such blood?
7. The character of the blood of dead, extinct, and even fossil animals, such as the mastodon, has been ascertained by obtaining and examining traces of it which had been shut up, perhaps for ages, in the circulatory canals of bone. A means of detecting blood in minute quantities is found in the spectroscope, the same instrument by which the constitution of the heavenly bodies has been studied. If a solution containing not more than one-thousandth part of a grain of the coloring matter of the corpuscle, be examined, this instrument will detect it.
8. White corpuscles? Total number of corpuscles in the body?
8. The corpuscles, just described, are known as the red blood corpuscles. Besides these, and floating along in the same plasma, are the white corpuscles. These are fewer in number, but larger and globular in form. They are colorless, and their motion is less rapid than that of the other variety. The total number of both varieties of these little bodies in the blood is enormous. It is calculated that in a cubic inch of that fluid there are eighty-three millions, and at least five hundred times that number in the whole body.
9. The blood in its natural condition in the body? Describe the process by which the coagulation of blood takes place?
9. Coagulation.—The blood, in its natural condition in the body, remains perfectly fluid; but, within a few minutes after its removal from its proper vessels, whether by accident or design, a change takes place. It begins to coagulate, or assume a semi-solid consistence. If allowed to stand, after several hours it separates into two distinct parts, one of them being a dark red jelly, the coagulum, or clot, which is heavy and sinks; and the other, a clear, straw-colored liquid, called serum, which covers the clot. This change is dependent upon the presence in the blood of fibrin, which possesses the property of solidifying under certain circumstances; one of these circumstances being when the blood is separated from living tissues. The color of the clot is due to the entanglement of the corpuscles with the fibrin.
10. If coagulation were impossible? How is it in fact?
10. In this law of the coagulation of the blood is our safeguard against death by hæmorrhage, or against undue loss of blood. If coagulation were impossible, the slightest injury in drawing blood would prove fatal. Whereas now, in vastly the larger proportion of cases, bleeding ceases spontaneously, because the blood, as it coagulates, stops the mouths of the injured blood-vessels. In another class of cases, where larger vessels are cut or torn, it is simply necessary to close them by a temporary pressure; for in a few minutes the clot will form and seal them up. In still more serious cases, where the blood-vessel is of large size, the surgeon is obliged to tie a "ligature" about it, and thus prevent the force of the blood-current from washing away the clots, which, forming within and around the vessel, would close it effectually.
11. What is worthy of remark? Coagulation of the blood of inferior animals? Of the blood of birds?
11. It is worthy of remark that this peculiarity is early implanted in the blood, even before birth, and in advance of any existing necessity for it; thus anticipating and guarding against danger. But this is not all. Of most of the inferior animals, which, as compared with man, are quite helpless, the blood coagulates more rapidly, and in the case of the birds, almost instantly. The relative composition of fluid and coagulated blood may be thus represented:
Fluid Blood. Coagulated Blood.
Plasma----------Serum---------Serum
\
\
--------Fibrin--------
\
\
Corpuscles------Corpuscles-------Clot.12. The blood, as a provider and purifier? What uses does the blood subserve? Experiments? Transfusion?
12. The Uses of the Blood.—The blood is the great provider and purifier of the body. It both carries new materials to all the tissues, and removes the worn out particles of matter. This is effected by the plasma. It both conveys oxygen and removes carbonic acid. This is done through the corpuscles. Some singular experiments have been tried to illustrate the life-giving power of the blood. An animal that has bled so freely as to be at the point of dying, is promptly brought back to life by an operation called transfusion, by which fresh blood from a living animal is injected into the blood-vessels of his body.
13. The case of the deaf and feeble dog? Horse? Dead dog?
13. It is related that a dog, deaf and feeble from age, had hearing and activity restored to him by the introduction into his veins of blood taken from a young dog; and, that a horse, twenty-six years old, having received the blood of four lambs acquired new vigor. And further, that a dog, just dead from an acute disease, was so far revived by transfusion, as to be able to stand and make a few movements.
14. Transfusion, as a fashionable remedy? What further of transfusion?
14. Transfusion has been practised upon man. At one time, shortly after Harvey's discovery of the "Circulation of the Blood," it became quite a fashionable remedy, it being thought possible by it to cure all forms of disease, and even to make the old young again. But these claims were soon found extravagant, and many unhappy accidents occurred in its practice; so that being forbidden by government and interdicted by the Pope, it rapidly fell into disuse. At the present time, however, it is sometimes resorted to in extreme cases, when there has been a great and rapid loss of blood; and there are upon record several instances where, other means having failed, life has been restored or prolonged by the operation of transfusion.
15. The seat of the reviving power of the blood? What further is related?
15. This reviving power of the blood seems to reside in the corpuscles; for transfusion, when attempted to be performed with the serum alone, has, in every case, proved fruitless. Now, though so much depends upon the blood and its corpuscles, it is a mistake to suppose that in them alone is the seat of life, or that they are, in an exclusive manner, alive. All the organs and parts of the body are mutually dependent one upon the other; and the complete usefulness of the blood, or of any other part, flows out of the harmonious action of all the parts.
16. Changes in the blood? What further is stated?
16. Change of Color.—The blood undergoes a variety of changes in its journey through the system. As it visits the different organs it both gives out and takes up materials. In one place it is enriched, in another it is impoverished. By reason of these alterations in its composition, the blood also changes its color. In one part of the body it is bright red, or arterial; in another it is dark blue, or venous. In the former case it is pure and fit for the support of the tissues; in the latter, it is impure and charged with effete materials. (The details of the change from dark to bright will be given in the chapter on Respiration.)
17. Motion of the blood? What is meant by the circulation of the blood? How confined? Discovery made by Harvey?
17. Circulation.—The blood is in constant motion during life. From the heart, as a centre, a current is always setting toward the different organs; and from these organs a current is constantly returning to the heart. In this way a ceaseless circular movement is kept up, which is called the Circulation of the Blood. This stream of the vital fluid is confined to certain fixed channels, the blood-vessels. Those branching from the heart are the arteries; those converging to it are the veins. The true course of the blood was unknown before the beginning of the seventeenth century. In 1619 it was discovered by the illustrious William Harvey. Like many other great discoverers, he suffered persecution and loss, but unlike some of them, he was fortunate enough to conquer and survive opposition. He lived long enough to see his discovery universally accepted, and himself honored as a benefactor of mankind.
Fig. 27.—The Organs of Circulation.
Fig. 28.—The Heart and Large Vessels.
A, Right Ventricle. B, Left Ventricle. C, Right Auricle. D, Left Auricle. E, Aorta. F, Pulmonary Artery.
18. Office of the heart? Location of the heart? Its beat? Its shape? Protection to the heart? What else is said in relation to the heart?
18. The Heart.—The heart is the central engine of the circulation. In this wonderful little organ, hardly larger than a man's fist, resides that sleepless force by which, during the whole of life, the current of the blood is kept in motion. It is placed in the middle and front part of the chest, inclining to the left side. The heartbeat may be felt and heard between the fifth and sixth ribs, near the breast-bone. The shape of the heart is conical, with the apex or point downward and in front. The base, which is upward, is attached so as to hold it securely in its place, while the apex is freely moveable. In order that loss of power from friction may be obviated, the heart is enclosed between two layers of serous membrane, which forms a kind of sac. This membrane is as smooth as satin, and itself secretes a fluid in sufficient quantities to keep it at all times well lubricated. The lining membrane of the heart, likewise, is extremely delicate and smooth.
Fig. 29.—Section of the Heart.
A, Right Ventricle. B, Left Ventricle. C, Right Auricle. D, Left Auricle. E, F, Inlets to the Ventricles. G, Pulmonary Artery. H, Aorta.
19. Formation of the heart? Right and left heart?
19. The Cavities of the Heart.—The heart is hollow, and so partitioned as to contain four chambers or cavities; two at the base, known as the auricles, from a fancied resemblance to the ear of a dog, and two at the apex or point, called ventricles. An auricle and a ventricle on the same side, communicate with each other, but there is no opening from side to side. It is customary to regard the heart as a double organ, and to speak of its division into the right and left heart. For while both halves act together in point of time, each half sustains an entirely distinct portion of the labor of the circulation. Thus, the right heart always carries the dark or venous blood, and the left always circulates the bright or arterial blood.
20. Capacity of the chambers of the heart? What wise provision is mentioned? The auricles?
20. If we examine the heart, we at once notice that though its various chambers have about the same capacity, the walls of the ventricles are thicker and stronger than those of the auricles. This is a wise provision, for it is by the powerful action of the former that the blood is forced to the most remote regions of the body. The auricles, on the contrary, need much less power, for they simply discharge their contents into the cavities of the heart near at hand and below them—into the ventricles.
21. Substance of the heart? Its fibres? Its movements? The advantage of such movements? Action of the heart? Its period of repose?
21. Action of the Heart.—The substance of the heart is of a deep red color, and its fibres resemble those of the voluntary muscles by which we move our bodies. But the heart's movements are entirely involuntary. The advantage of this is evident; for if it depended upon us to will each movement, our entire attention would be thus engaged, and we would find no time for study, pleasure, or even sleep. The action of the heart consists in alternate contractions and dilatations. During contraction the walls come forcibly together, and thus drive out the blood. In dilatation, they expand and receive a renewed supply. These movements are called systole and diastole. The latter may be called the heart's period of repose; and although it lasts only during two-fifths of a heart-beat, or about a third of a second, yet during the day it amounts to more than nine hours of total rest.
22. Remarkable property of the tissue of the heart? How shown? How interesting? In cold-blooded animals? Heart of a turtle? Of a frog? Alligator?
22. A remarkable property of the tissue of the heart is its intense vitality. For while it is more constantly active than any other organ of the body, it is the last to part with its vital energy. This is especially interesting in view of the fact that after life is apparently extinguished, as from drowning, or poisoning by chloroform, there yet lingers a spark of vitality in the heart, which, by continued effort, may be fanned into a flame so as to revivify the whole body. In cold-blooded animals this irritability of the heart is especially remarkable. The heart of a turtle will pulsate, and the blood circulate for a week after its head has been cut off; and the heart will throb regularly many hours after being cut out from the creature's chest. The heart of a frog or serpent, separated entirely from the body, will contract at the end of ten or twelve hours: that of an alligator has been known to beat twenty-eight hours after the death of the animal.
23. Course of the blood through the heart? Course of heart-currents?
23. Passage of the Blood through the Heart.—Let us now trace the course of the blood through the several cavities of the heart. In the first place, the venous blood, rendered dark and impure by contact with the changing tissues of the body, returns to the right heart by the veins. It enters and fills the right auricle during its dilatation: the auricle then contracts and fills the right ventricle. Almost instantly, the ventricle contracts forcibly and hurries the blood along the great artery of the lungs, to be purified in those organs. Secondly, having completed the circuit of the lungs, the pure and bright arterial blood enters the left auricle. This now contracts and fills the left ventricle, which cavity, in its turn, contracts and sends the blood forth on its journey again through the system. This general direction from right to left is the uniform and undeviating course of heart-currents.
24. Openings of the ventricles? How guarded? How do the valves operate? The consequence? Heart-sounds?
24. The mechanism which enforces and regulates it, is as simple as it is beautiful. Each ventricle has two openings, an inlet and an outlet, each of which is guarded by strong curtains, or valves. These valves open freely to admit the blood entering from the right, but close inflexibly against its return. Thus, when the auricle contracts, the inlet valve opens; but as soon as the ventricle begins to contract, it closes promptly. The contents are then, so to speak, cornered, and have but one avenue of escape, that through the outlet valve into the arteries beyond. As soon as the ventricle begins to dilate again, this valve shuts tightly and obstructs the passage. The closing of these valves occasions the two heart-sounds, which we hear at the front of the chest.
25. Heart-beats? The heart as a susceptible organ? Heat, exercise, etc.? Posture?
25. Frequency of the Heart's Action.—The alternation of contraction and dilation constitutes the heartbeats. These follow each other not only with great regularity, but with great rapidity. The average number in an adult man is about seventy-two in a minute. But the heart is a susceptible organ, and many circumstances affect its rate of action. Heat, exercise, and food will increase its action, as cold, fasting, and sleep will decrease it. Posture, too, has a curious influence; for if while sitting, the beats of the heart number seventy-one; standing erect will increase them to eighty-one, and lying down will lower them to sixty-six.
26. Mental emotions? Sudden excitement? Excessive joy? The heart-beat rate? Bonaparte and Wellington?
26. The modifying influence of mental emotions is very powerful. Sudden excitement of feeling will cause the heart to palpitate, or throb violently. Depressing emotions sometimes temporarily interrupt its movements, and the person faints in consequence. Excessive joy, grief, or fear, has occasionally suspended the heart's action entirely, and thus caused death. The rate of the heart-beat may be naturally above or below seventy-two. Thus it is stated that the pulse of the savage is always slower than that of the civilized man. Bonaparte and Wellington were very much alike in their heart's pulsations, which were less than fifty in the case of each.
27. Average number of heart-beats? In one hour? Year? Lifetime?
27. Activity of the Heart.—The average number of heart-beats during a lifetime may be considered as at the rate of seventy-two per minute, although this estimate is probably low; for during several years of early life the rate is above one hundred a minute. In one hour, then, the heart pulsates four thousand times; in a day, one hundred thousand times; and in a year, nearly thirty-eight million times. If we compute the number during a lifetime, thirty-nine years being the present average longevity of civilized mankind, we obtain as the vast aggregate, fourteen hundred millions of pulsations.
28. Amount of blood expelled? Theories of the ancients?
28. Again, if we estimate the amount of blood expelled by each contraction of the ventricles, at four ounces, then the weight of the blood moved during one minute will amount to eighteen pounds. In a day it will be about twelve tons; in a year, four thousand tons; and in the course of a lifetime, over one hundred and fifty thousand tons. These large figures indicate, in some measure, the immense labor necessary to carry on the interior and vital operations of our bodies. In this connection, we call to mind the fanciful theories of the ancients in reference to the uses of the heart. They regarded it as the abode of the soul, and the source of the nobler emotions—bravery, generosity, mercy, and love. The words courage and cordiality are derived from a Latin word signifying heart. Many other words and phrases, as hearty, heart-felt, to learn by heart, and large-hearted, show how tenaciously these exploded opinions have fastened themselves upon our language.
29. The tendency at the present time? Why is this view inadequate?
29. At the present time the tendency is to ascribe purely mechanical functions to the heart. This view, like the older one, is inadequate; for it expresses only a small part of our knowledge of this organ. The heart is unlike a simple machine, because its motive power is not applied from without, but resides in its own substance. Moreover, it repairs its own waste, it lubricates its own action, and it modifies its movements according to the varying needs of the system. It is more than a mere force-pump, just as the stomach is something more than a crucible, and the eye something more than an optical instrument.
30. What are the arteries? Their walls? Their membrane?
30. The Arteries.—The tube-like canals which carry the blood away from the heart are the arteries. Their walls are made of tough, fibrous materials, so that they sustain the mighty impulse of the heart, and are not ruptured. In common with the heart, the arteries have a delicately smooth lining membrane. They are also elastic, and thus re-enforce the action of the heart: they always remain open when cut across, and after death are always found empty.
31. Early anatomists? The service of the illustration?
31. The early anatomists observed this phenomenon, and supposing that the same condition existed during life, came to the conclusion that these tubes were designed to act as air-vessels, hence the name artery, from a Greek word which signifies containing air. This circumstance affords us an illustration of the confused notions of the ancients in reference to the internal operations of the body. Cicero speaks of the arteries as "conveying the breath to all parts of the body."
32. The arterial system? The branches and sub-branches of the arteries?
32. The arterial system springs from the heart by a single trunk, like a minute and hollow tree, with numberless branches. As these branches leave the heart they divide and subdivide, continually growing smaller and smaller, until they can no longer be traced with the naked eye. If, then, we continue the examination by the aid of a microscope, we see these small branches sending off still smaller ones, until all the organs of the body are penetrated by arteries.
33. Successive undulations from the heart? Course of the arteries? Protection of the arteries? General location of the arteries?
33. The Pulse.—With each contraction of the left heart, the impulse causes a wave-like motion to traverse the entire arterial system. If the arteries were exposed to view, we might see successive undulations speeding from the heart to the smallest of the branches, in about one-sixth part of a second. The general course of the arteries is as far as possible from the surface. This arrangement is certainly wise, as it renders them less liable to injury, the wounding of an artery being especially dangerous. It also protects the arteries from external and unequal pressure, by which the force of the heart would be counteracted and wasted. Accordingly, we generally find these vessels hugging close to the bones, or hiding behind the muscles and within the cavities of the body.
34. Where do the arteries lie? If we apply the finger? Pulse? Where felt?
34. In a few situations, however, the arteries lie near the surface; and if we apply the finger to any of these parts, we will distinctly feel the movement described, taking place in harmony with the heart-beat. This is part of the wave-motion just mentioned, and is known as the pulse. All are more familiar with the pulse at the wrist, in the radial artery; but the pulse is not peculiar to that position, for it may be felt in the carotid of the neck, in the temporal at the temple, and elsewhere, especially near the joints.
Fig. 30.—The Form of the Pulse.
35. The pulse as an index? Of what does it inform the physician? Instrument for recording pulsation?
35. Since the heart-beat makes the pulse, whatever affects the former affects the latter also. Accordingly, the pulse is a good index of the state of the health, so far as the health depends upon the action of the heart. It informs the physician of the condition of the circulation in four particulars: its rate, regularity, force, and fullness; and nearly every disease modifies in some respect the condition of the pulse. A very ingenious instrument, known as the sphygmograph, or pulse-writer, has recently been invented, by the aid of which the pulse is made to write upon paper its own signature, or rather to sketch its own profile. This instrument shows with great accuracy the difference between the pulses of health and those of disease. In Fig. 30 is traced the form of the pulse in health, which should be read from left to right. That part of the trace which is nearly perpendicular coincides with the contraction of the ventricles; while the wavy portion marks their dilatation.
36. What are the veins? How do they form? What do they resemble?
36. The Veins.—The vessels which convey the blood on its return to the heart are the veins. They begin in the several organs of the body, and at first are extremely small; but uniting together as they advance, they constantly increase in size, reminding us of the way in which the fine rootlets of the plant join together to form the large roots, or of the rills and rivulets that flow together to form the large streams and rivers. In structure, the veins resemble the arteries, but their walls are comparatively inelastic. They are more numerous, and communicate with each other freely in their course, by means of interlacing branches.
Fig. 31.—The Valves of the Veins.
37. Valves in the veins? What are they? Their position? Experiment with the cord?
37. But the chief point of distinction is in the presence of the valves in the veins. These are little folds of membrane, disposed in such a way, that they only open to receive blood flowing toward the heart, and close against a current in the opposite direction. Their position in the veins on the back of the hand may be readily observed, if we first obstruct the return of blood by a cord tied around the forearm or wrist. In a few minutes the veins will appear swollen, and upon them will be seen certain prominences, about an inch apart. These latter indicate the location of the valves, or, rather, they show that the vessels in front of the valves are distended by the blood, which cannot force a passage back through them.
38. What will be proved by the experiment? What inference is drawn?
38. This simple experiment proves that the true direction of the venous blood is toward the heart. That the color of the blood is dark, will be evident, if we compare the hand thus bound by a cord with the hand not so bound. It also proves that the veins lie superficially, while the arteries are beneath the muscles, well protected from pressure; and that free communication exists from one vein to another. If now we test the temperature of the constricted member by means of a thermometer, we will find that it is colder than natural, although the amount of blood is larger than usual. From this fact we infer, that whatever impedes the venous circulation tends to diminish vitality; and hence, articles of clothing or constrained postures, that confine the body or limbs, and hinder the circulation of the blood, are to be avoided as injurious to the health.
39. Capillaries? How regarded? Harvey?
39. The Capillaries.—A third set of vessels completes the list of the organs of the circulation, namely, the capillary vessels, so called (from the Latin word capillaris, hair-like), because of their extreme fineness. They are, however, smaller than any hair, having a diameter of about 1/3000 of an inch, and can only be observed by the use of the microscope. These vessels may be regarded as the connecting link between the last of the arteries and the first of the veins. The existence of these vessels was unknown to Harvey, and was the one step wanting to complete his great work. The capillaries were not discovered until 1661, a short time after the invention of the microscope.
40. The circulation of the blood in the web of a frog's foot? Describe it. How general is the existence of the tissues?
40. The circulation of the blood, as seen under the microscope, in the transparent web of a frog's foot, is a spectacle of rare beauty, possessing more than ordinary interest, when we consider that something very similar is taking place in our own bodies, on a most magnificent scale. It is like opening a secret page in the history of our own frames. We there see distinctly the three classes of vessels with their moving contents; first, the artery, with its torrent of blood rushing down from the heart, secondly, the vein, with its slow, steady stream flowing in the opposite direction; and between them lies the network of capillaries, so fine that the corpuscles can only pass through "in single file." The current has here an uncertain or swaying motion, hurrying first in one direction, then hesitating, and then turning back in the opposite direction, and sometimes the capillaries contract so as to be entirely empty. Certain of the tissues are destitute of capillaries; such are cartilage, hair, and a few others on the exterior of the body. In all other structures, networks of these vessels are spread out in countless numbers: so abundant is the supply, that it is almost impossible to puncture any part with the point of a needle without lacerating tens, or even hundreds of these vessels.
Fig. 33.—Margin of Frog's Web magnified 30 diameters.
Fig. 32.—Web of a Frog's Foot, slightly magnified.
41. Elasticity of the capillaries? Grain of sand in the eye? Blush? Other cases?
41. The capillaries are elastic, and may so expand as to produce an effect visible to the naked eye. If a grain of sand, or some other foreign particle, lodge in the eye, it will become irritated, and in a short time the white of the eye will be "blood-shot." This appearance is due to an increase in the size of these vessels. A blush is another example of this, but the excitement comes through the nervous system, and the cause is some transient emotion, either of pleasure or pain. Another example is sometimes seen in purplish faces of men addicted to drinking brandy; in them the condition is a congestion of the capillary circulation, and is permanent, the vessels having lost their power of elastic contraction.
42. Show what time is required for a given portion of blood to travel once around the body.
42. Rapidity of the Circulation.—That the blood moves with great rapidity is evident from the almost instant effects of certain poisons, as prussic acid, which act through the blood. Experiments upon the horse, dog, and other inferior animals, have been made to measure its velocity. If a substance, which is capable of a distinct chemical reaction (as potassium ferrocyanide, or barium nitrate), be introduced into a vein of a horse on one side, and blood be taken from a distant vein on the other side, its presence may be detected at the end of twenty or thirty-two seconds. In man, the blood moves with greater speed, and the circuit is completed in twenty-four seconds.
43. Time required for all the blood to circulate completely around?
43. What length of time is required for all the blood of the body to make a complete round of the circulation? This question cannot be answered with absolute accuracy, since the amount of the blood is subject to continual variations. But, if we assume this to be one-eighth of the weight of the body, about eighteen pounds, it will be sufficiently correct for our purpose. Now to complete the circuit, this blood must pass once through the left ventricle, the capacity of which is two ounces. Accordingly, we find that, under ordinary circumstances, all the blood makes one complete rotation every two minutes; passing successively through the heart, the capillaries of the lungs, the arteries, the capillaries of the extremities, and through the veins.
44. What is meant by assimilation? What can you say of its use, etc.? Time?
44. Assimilation.—The crowning act of the circulation, the furnishing of supplies to the different parts of the body, is effected by means of the capillaries. The organs have been wasted by use; the blood has been enriched by the products of digestion. Here, within the meshes of the capillary network, the needy tissues and the needed nutriment are brought together. By some mysterious chemistry, each tissue selects and withdraws from the blood the materials it requires, and converts them into a substance like itself. This conversion of lifeless food into living tissue is called assimilation. The process probably takes place at all times, but the period especially favorable for it is during sleep. Then the circulation is slower, and more regular, and most of the functions are at rest. The body is then like some trusty ship, which after a long voyage is "hauled up for repairs."
45. What is stated of the injuries to the blood-vessels?
45. Injuries to the Blood-vessels.—It is important to be able to discriminate between an artery and a vein, in the case of a wound, and if we remember the physiology of the circulation we may readily do so. For, as we have already seen, hæmorrhage from an artery is much more dangerous than that from a vein. The latter tends to cease spontaneously after a short time. The arterial blood flows away from the heart with considerable force, in jets; its color being bright scarlet. The venous blood flows toward the heart from that side of the wound furthest from the heart; its stream being continuous and sluggish; its color dark. In an injury to an artery, pressure should be made between the heart and the wound; and in the case of a vein that persistently bleeds, it should be made upon the vessel beyond its point of injury.
QUESTIONS FOR TOPICAL REVIEW.
PAGE 1. In what organisms is the so-called circulatory fluid found? [101] 2. How is it designated in the different organisms? [101] 3. What can you state of the importance of blood to the body? [101], [105] 4. Of its great abundance, color, and composition? [101], [102], [107] 5. Describe the corpuscles of the human blood. [102], [103], [104] 6. What is said of them in comparison with those of the lower animals? [103] 7. Of the importance of sometimes detecting human from other blood? [103] 8. What means have we of detecting blood in spots or stains? [103], [104] 9. What is meant by coagulation of the blood? [104] 10. What wisdom is there in the law of the blood's coagulation? [104], 105 11. How is this wisdom made manifest? [105] 12. In what cases is the aid of the surgeon required? [105] 13. What are the two great uses of the blood? [105] 14. Through what mediums is the blood provided with new material and relieved of the old material? [105] 15. What do you understand by the operation called transfusion? [106] 16. What cases of transfusion are reported of the lower animals? [106] 17. What can you state of transfusion as practised upon man? [106] 18. What further can you say on the subject? [106], [107] 19. What changes take place in the color of the blood in its journey through the system? [107] 20. State all you can in relation to the circulation of the blood. [107] 21. All, in relation to the size, shape, and location of the heart. [107], [109] 22. How is the loss of power in the heart movements obviated? [109] 23. Give a description of the formation of the heart. [109], [110], [111] 24. What can you state of the ventricles and auricles of the heart? [110] 25. Describe the action of the heart. [111] 26. What special vitality does the tissue of the heart possess? [111] 27. State all you can on the subject. [111] 28. Describe the course of the blood through the cavities of the heart. [112] 29. Describe the mechanism that regulates the heart-currents. [112] 30. How do you account for the two heart-sounds at the front of the chest? [112] 31. State what you can of the frequency of the heart's action. [112], [113] 32. Of the activity of the heart. [113], [114] 33. What do you understand by the arteries? [114], [115] 34. State what you can of the arteries and the arterial system. [114], [115] 35. What do you understand by the pulse? [115], [116] 36. In what part of the body may the pulse be felt? [116] 37. What further can you state of the pulse? [116], [117] 38. What are the veins? [117] 39. Where do they exist, and how are they formed? [117] 40. Describe the valves of the veins and their uses. [117] 41. Now give a full description of the construction of the veins. [117] 42. What further can you state of the veins? [117], [118] 43. What do you understand by the capillaries? [118], [119] 44. What service do the capillaries perform? [118], [119], [121] 45. Describe the circulation of the blood in the region of the heart. [118], [119] 46. What can you state of the rapidity of the blood's circulation? [120] 47. Of the process known as assimilation? [121] 48. Of injuries to the blood-vessels? [121]
CHAPTER VIII.
RESPIRATION.
The Objects of Respiration—The Lungs—The Air-Passages—The Movements of Respiration—Expiration and Inspiration—The Frequency of Respiration—Capacity of the Lungs—The Air we breathe—Changes in the Air from Respiration—Changes in the Blood—Interchange of Gases in the Lungs—Comparison between Arterial and Venous Blood—Respiratory Labor—Impurities of the Air—Dust—Carbonic Acid—Effects of Impure Air—Nature's Provision for Purifying the Air—Ventilation—Animal Heat—Spontaneous Combustion.
| PAGE | |
| 1. In what organisms is the so-called circulatory fluid found? | [101] |
| 2. How is it designated in the different organisms? | [101] |
| 3. What can you state of the importance of blood to the body? | [101], [105] |
| 4. Of its great abundance, color, and composition? | [101], [102], [107] |
| 5. Describe the corpuscles of the human blood. | [102], [103], [104] |
| 6. What is said of them in comparison with those of the lower animals? | [103] |
| 7. Of the importance of sometimes detecting human from other blood? | [103] |
| 8. What means have we of detecting blood in spots or stains? | [103], [104] |
| 9. What is meant by coagulation of the blood? | [104] |
| 10. What wisdom is there in the law of the blood's coagulation? | [104], 105 |
| 11. How is this wisdom made manifest? | [105] |
| 12. In what cases is the aid of the surgeon required? | [105] |
| 13. What are the two great uses of the blood? | [105] |
| 14. Through what mediums is the blood provided with new material and relieved of the old material? | [105] |
| 15. What do you understand by the operation called transfusion? | [106] |
| 16. What cases of transfusion are reported of the lower animals? | [106] |
| 17. What can you state of transfusion as practised upon man? | [106] |
| 18. What further can you say on the subject? | [106], [107] |
| 19. What changes take place in the color of the blood in its journey through the system? | [107] |
| 20. State all you can in relation to the circulation of the blood. | [107] |
| 21. All, in relation to the size, shape, and location of the heart. | [107], [109] |
| 22. How is the loss of power in the heart movements obviated? | [109] |
| 23. Give a description of the formation of the heart. | [109], [110], [111] |
| 24. What can you state of the ventricles and auricles of the heart? | [110] |
| 25. Describe the action of the heart. | [111] |
| 26. What special vitality does the tissue of the heart possess? | [111] |
| 27. State all you can on the subject. | [111] |
| 28. Describe the course of the blood through the cavities of the heart. | [112] |
| 29. Describe the mechanism that regulates the heart-currents. | [112] |
| 30. How do you account for the two heart-sounds at the front of the chest? | [112] |
| 31. State what you can of the frequency of the heart's action. | [112], [113] |
| 32. Of the activity of the heart. | [113], [114] |
| 33. What do you understand by the arteries? | [114], [115] |
| 34. State what you can of the arteries and the arterial system. | [114], [115] |
| 35. What do you understand by the pulse? | [115], [116] |
| 36. In what part of the body may the pulse be felt? | [116] |
| 37. What further can you state of the pulse? | [116], [117] |
| 38. What are the veins? | [117] |
| 39. Where do they exist, and how are they formed? | [117] |
| 40. Describe the valves of the veins and their uses. | [117] |
| 41. Now give a full description of the construction of the veins. | [117] |
| 42. What further can you state of the veins? | [117], [118] |
| 43. What do you understand by the capillaries? | [118], [119] |
| 44. What service do the capillaries perform? | [118], [119], [121] |
| 45. Describe the circulation of the blood in the region of the heart. | [118], [119] |
| 46. What can you state of the rapidity of the blood's circulation? | [120] |
| 47. Of the process known as assimilation? | [121] |
| 48. Of injuries to the blood-vessels? | [121] |
The Objects of Respiration—The Lungs—The Air-Passages—The Movements of Respiration—Expiration and Inspiration—The Frequency of Respiration—Capacity of the Lungs—The Air we breathe—Changes in the Air from Respiration—Changes in the Blood—Interchange of Gases in the Lungs—Comparison between Arterial and Venous Blood—Respiratory Labor—Impurities of the Air—Dust—Carbonic Acid—Effects of Impure Air—Nature's Provision for Purifying the Air—Ventilation—Animal Heat—Spontaneous Combustion.
1. Difference between the two sets of capillaries? Change effected by respiration or breathing?
1. The Object of Respiration.—In one set of capillaries, or hair-like vessels, the blood is impoverished for the support of the different members and organs of the body. In another capillary system the blood is refreshed and again made fit to sustain life. The former belongs to the greater or systemic circulation; the latter to the lesser or pulmonary, so called from pulmo, the lungs, in which organs it is situated. The blood, as sent from the right side of the heart to the lungs, is venous, dark, impure, and of a nature unfit to circulate again through the tissues. But, when the blood returns from the lungs to the left side of the heart, it has become arterial, bright, pure, and no longer hurtful to the tissues. This marvellous purifying change is effected by means of the very familiar act of respiration, or breathing.
2. What are the lungs? How many lungs are there? Lung-substance? Its properties? The pleura?
2. The Lungs.—The lungs are the special organs of respiration. There are two of them, one on each side of the chest, which cavity they, with the heart, almost wholly occupy. The lung-substance is soft, elastic, and sponge-like. Under pressure of the finger, it crepitates, or crackles, and floats when thrown into water; these properties being due to the presence of air in the minute air-cells of the lungs. To facilitate the movements necessary to these organs, each of them is provided with a double covering of an exceedingly smooth and delicate membrane, called the pleura. One layer of the pleura is attached to the walls of the chest, and the other to the lungs; and they glide, one upon the other, with utmost freedom. Like the membrane which envelops the heart, the pleura secretes its own lubricating fluid, in quantities sufficient to keep it always moist.
Fig. 34.—Organs of the Chest.
A, Lungs. B, Heart. D, Pulmonary Artery. E, Trachea.
Fig. 36.—Diagram and Section of the Air-cells.
Fig. 35.—Larynx, Trachea, and Bronchial Tubes.
3. Communication of the lungs with the external air? Bronchial tubes?
3. The Air-Passages. —The lungs communicate with the external air by means of certain air-tubes, the longest of which, the trachea, or windpipe, runs along the front of the neck (Fig. 34, E, and 35). Within the chest this tube divides into two branches, one entering each lung; these in turn give rise to numerous branches, or bronchial tubes, as they are called, which gradually diminish in size until they are about one-twenty-fifth of an inch in diameter. Each of these terminates in a cluster of little pouches, or "air-cells," having very thin walls, and covered with a capillary network, the most intricate in the body (Fig. 36).
4. Office of the bronchial tubes? What further can you state of them?
4. These tubes are somewhat flexible, sufficiently so to bend when the parts move in which they are situated; but they are greatly strengthened by bands or rings of cartilage which keep the passages always open; otherwise there would be a constantly-recurring tendency to collapse after every breath. The lung-substance essentially consists of these bronchial tubes and terminal air-cells, with the blood-vessels ramifying about them (Fig. 37). At the top of the trachea is the larynx, a sort of box of cartilage, across which are stretched the vocal cords. Here the voice is produced chiefly by the passage of the respired air over these cords, causing them to vibrate.
Fig. 37.—Section of the Lungs.
5. The epiglottis? When it does not close in time, what is the consequence?
5. Over the opening of the larynx is found the epiglottis, which fits like the lid of a box at the entrance to the lungs, and closes during the act of swallowing, so that food and drink shall pass backward to the œsophagus, or gullet (Fig. 38). Occasionally it does not close in time, and some substance intrudes within the larynx, when we at once discover, by a choking sensation, that "something has gone the wrong way," and, by coughing, we attempt to expel the unwelcome intruder. The epiglottis is one of the many safeguards furnished by nature for our security and comfort, and is planned and put in place long before these organs are brought into actual use in breathing and in taking food.
Fig. 38.—Section of Mouth and Throat.
A, The Tongue. B, The Uvula C, Vocal Cord. E, Epiglottis. L, Larynx. N, Trachea. O, Œsophagus.
6. Lining of the air-passages? Ciliated cells? Their uses? The three diseases of the lungs?
Fig. 39.—Ciliated Cells.
6. The air-passages are lined through nearly their whole extent with mucous membrane, which maintains these parts in a constantly moist condition. This membrane has a peculiar kind of cells upon its outer surface. If examined under a powerful microscope, we may see, even for a considerable time after their removal from the body, that these cells have minute hair-like processes in motion, which wave like a field of grain under the influence of a breeze (Fig. 39). This is a truly beautiful sight; and since it is found that these little cilia, as they are called, always produce currents in one direction, from within outward, it is probable that they serve a useful purpose in catching and carrying away from the lungs dust and other small particles drawn in with the breath (Fig. 39). The three diseases which more commonly affect the lungs, as the result of exposure, are pneumonia, or inflammation of the lungs, implicating principally the air-cells; bronchitis, an inflammation of the large bronchial tubes; and pleurisy, an inflammation of the investing membrane of the lungs, or pleura. Among the young, an affection of the trachea takes place, known as croup.
7. The act of breathing? Extension of the chest by breathing?
7. The Movements of Respiration.—The act of breathing has two parts—(1), inspiration, or drawing air into the lungs, and (2), expiration, or expelling it from the lungs again. In inspiration, the chest extends in its length, breadth, and height, or width. We can prove that this is the case as regards the two latter, by observing the effect of a deep breath. The ribs are elevated by means of numerous muscles, some of which occupy the entire spaces between those bones. But the increase in length, or vertically, is not so apparent, as it is caused by a muscle within the body called the diaphragm, it being the thin partition which separates the chest from the abdomen, rising like a dome within the chest. (Fig. 16).
8. Contraction of the diaphragm? Power of the diaphragm? Effects of extending the walls of the chest? The habit of taking frequent and deep inspirations?
8. With every inspiration, the diaphragm contracts, and in so doing, approaches more nearly a plane, or horizontal, surface, and thus enlarges the capacity of the chest. Laughing, sobbing, hiccoughing, and sneezing are caused by the spasmodic or sudden contraction of the diaphragm. The special power of this muscle is important in securing endurance, or "long wind," as it is commonly expressed; which may be obtained mainly by practice. It is possessed in a marked degree by the mountaineer, the oarsman, and the trained singer. As the walls of the chest extend, the lungs expand, and the air rushes in to fill them. This constitutes an inspiration. The habit of taking frequent and deep inspirations, in the erect position, with the shoulders thrown back, tends greatly to increase the capacity and power of the organs of respiration.
9. Expiration? The mechanism of expiration?
9. Expiration is a less powerful act than inspiration. The diaphragm relaxes its contraction, and ascends in the form of a dome; the ribs descend and contract the chest; while the lungs themselves, being elastic, assist to drive out the air. The latter passes out through the same channels by which it entered. At the end of each expiration there is a pause, or period of repose, lasting about as long as the period of action.
10. Frequency of respiration? Effect of hurried action of the heart?
10. Frequency of Respiration.—It is usually estimated that we breathe once during every four beats of the heart, or about eighteen times in a minute. There is, of course, a close relation between the heart and lungs, and whatever modifies the pulse, in like manner affects the breathing. When the action of the heart is hurried, a larger amount of blood is sent to the lungs, and, as the consequence, they must act more rapidly. Occasionally, the heart beats so very forcibly that the lungs cannot keep pace with it, and then we experience a peculiar sense of distress from the want of air. This takes place when we run until we are "out of breath." At the end of every fifth or sixth breath, the inspiration is generally longer than usual, the effect being to change more completely the air of the lungs.
11. Respiration controlled by the will? Advantage of the knowledge to us?
11. Although, as a general rule, the work of respiration goes on unconsciously and without exertion on our part, it is nevertheless under the control of the will. We can increase or diminish the frequency of its acts at pleasure, and we can "hold the breath," or arrest it altogether for a short time. From twenty to thirty seconds is ordinarily the longest period in which the breath can be held; but if we first expel all the impure air from the lungs, by taking several very deep inspirations, the time may be extended to one and a half or even two minutes. This should be remembered, and acted upon, before passing through a burning building, or any place where the air is very foul. The arrest of the respiration may be still further prolonged by training and habit; thus it is said, the pearl-fishers of India can remain three or four minutes under water without being compelled to breathe.
12. Capacity of the lungs? Time required to renovate the air in the lungs? In tranquil respiration? Importance of the provision?
12. Capacity of the Lungs.—The lungs are not filled and emptied by each respiration. For while their full capacity, in the adult, is three hundred and twenty cubic inches, or more than a gallon, the ordinary breathing air is only one-sixteenth part of that volume, or twenty cubic inches, being two-thirds of a pint. Accordingly, a complete renovation, or rotation, of the air of the lungs does not take place more frequently than about once in a minute; and by the gradual introduction of the external air, its temperature is considerably elevated before it reaches the delicate pulmonary capillaries. In tranquil respiration, less than two-thirds of the breathing power is called into exercise, leaving a reserve capacity of about one hundred and twenty cubic inches, equivalent to three and one half pints. This provision is indispensable to the continuation of life; otherwise, a slight embarrassment of respiration, by an ordinary cold, for instance, would suffice to cut off the necessary air, and the spark of life would be speedily extinguished.
13. The atmosphere? How high or deep? How essential to life? Marine life in perfectly pure water and air?
13. The Air we breathe.—The earth is enveloped on all sides by an invisible fluid, called the atmosphere. It forms a vast and shoreless ocean of air, forty-five miles deep, encircling and pervading all objects on the earth's surface, which is absolutely essential for the preservation of all vegetable and animal life,—in the sea, as well as on the land and in the air. At the bottom, or in the lower strata of this aerial ocean, we move and have our being. Perfectly pure water will not support marine life, for a fish may be drowned in water from which the air has been exhausted, just as certainly as a mouse, or any other land animal, will perish if put deeply into the water for a length of time. The cause is the same in both cases: the animal is deprived of the requisite amount of air. It is also stated, that if the water-supply of the plant be deprived of air, its vital processes are at once checked.
14. Composition of the air? Properties of the two gases?
14. The air is not a simple element, as the ancients supposed, but is formed by the mingling of two gases, known to the chemist as oxygen and nitrogen, in the proportion of one part of the former to four parts of the latter. These gases are very unlike, being almost opposite in their properties: nitrogen is weak, inert, and cannot support life; while oxygen is powerful, and incessantly active; and is the essential element which gives to the atmosphere its power to support life and combustion. The discovery of this fact was made by the French chemist, Lavoisier, in 1778.
15. Air once breathed? An animal in it? A candle? Analysis of expired air? Change in volume?
15. Changes in the Air from Respiration.—Air that has been once breathed is no longer fit for respiration. An animal confined within it will sooner or later die; so too, a lighted candle placed in it will be at once extinguished. If we collect a quantity of expired air and analyze it, we shall find that its composition is not the same as that of the inspired air. When the air entered the lungs it was rich in oxygen; now it contains twenty-five per cent. less of that gas. Its volume, however, remains nearly the same; its loss being replaced by another and very different gas, which the lungs exhaled, called carbonic acid, or, as the chemist terms it, carbon dioxide.
16. What else has the expired air gained? When and where noticed?
16. The expired air has also gained moisture. This is noticed when we breathe upon a mirror, or the window-pane, the surface being tarnished by the condensation of the watery vapor exhaled by the lungs. In cold weather, this causes the fine cloud which is seen issuing from the nostrils or mouth with each expiration, and contributes in forming the feathery crystals of ice which decorate our window-panes on a winter's morning.
17. Nature of the watery vapor? Its effects upon animals?
17. This watery vapor contains a variable quantity of animal matter, the exact nature of which is unknown; but when collected it speedily putrefies and becomes highly offensive. From the effects, upon small animals, of confinement in their own exhalations, having at the same time an abundant supply of fresh air, it is believed that the organic matters thrown off by the lungs and skin are direct and active poisons; and that to such emanations from the body, more than to any other cause, are due the depressing and even fatal results which follow the crowding of large numbers of persons into places of limited capacity.
18. Give some of the instances furnished by history.
18. History furnishes many painful instances of the ill effects of overcrowding. In 1756, of one hundred and forty-six Englishmen imprisoned in the Black Hole of Calcutta, only twenty-three, at the end of eight hours, survived. After the battle of Austerlitz, three hundred prisoners were crowded into a cavern, where, in a few hours, two-thirds of their number died. On board a steam-ship, during a stormy night, one hundred and fifty passengers were confined in a small cabin, but when morning came, only eighty remained alive.
19. Change in the blood from blue to red. Upon what does the change depend? How shown?
19. Changes in the Blood from Respiration.—The most striking change which the blood undergoes by its passage through the lungs, is the change of color from a dark blue to bright red. That this change is dependent upon respiration has been fully proved by experiment. If the trachea, or windpipe, of a living animal be so compressed as to exclude the air from the lungs, the blood in the arteries will gradually grow darker, until its color is the same as that of the venous blood. When the pressure is removed the blood speedily resumes its bright hue. Again, if the animal be made to breathe an atmosphere containing more oxygen than atmospheric air, the color changes from scarlet to vermilion, and becomes even brighter than arterial blood. This change of color is not of itself a very important matter, but it indicates a most important change of composition.
20. What does the air lose and gain by respiration? What, the blood? Air as food?
20. The air, as we have seen, by respiration loses oxygen and gains carbonic acid: the blood, on the contrary, gains oxygen and loses carbonic acid. The oxygen is the food of the blood corpuscles; while the articles we eat and drink belong more particularly to the plasma of the blood. The air, then, it is plain, is a sort of food, and we should undoubtedly so regard it, if it were not for the fact that we require it constantly, instead of taking it at stated intervals, as is the case with our articles of diet. Again, as the demand of the system for food is expressed by the sensation of hunger, so the demand for air is marked by a painful sensation called suffocation.
21. Moist animal membranes? How shown with the bladder?
21. Interchange of Gases in the Lungs.—As the air and the blood are not in contact, they being separated from each other by the walls of the air-cells and of the blood-vessels, how can the two gases, oxygen and carbonic acid, exchange places? Moist animal membranes have a property which enables them to transmit gases through their substance, although they are impervious to liquids. This may be beautifully shown by suspending a bladder containing dark blood in a jar of oxygen. At the end of a few hours the oxygen will have disappeared, the blood will be brighter in color, and carbonic acid will be found in the jar.
22. Gaseous diffusion? If oxygen be not received? If carbonic acid be retained?
22. If this interchange takes place outside of the body, how much more perfectly must it take place within, where it is favored by many additional circumstances! The walls of the vessels and the air-cells offer no obstacle to this process, which is known as gaseous diffusion. Both parts of the process are alike of vital importance. If oxygen be not received, the organs cease to act; and if carbonic acid be retained in the blood, its action is that of a poison; unconsciousness, convulsions, and death following.
23. Difference in the appearance and composition of the blood? Temperature of the blood? The blood while passing through the lungs? The consequence?
23. Difference between Arterial and Venous Blood.—The following table presents the essential points of difference in the appearance and composition of the blood, before and after its passage through the lungs:—
Venous Blood. Arterial Blood. Color, Dark blue, Scarlet. Oxygen, 8 per cent., 18 per cent. Carbonic Acid, 15 to 20 per cent., 6 per cent., or less. Water, More, Less. The temperature of the blood varies considerably; but the arterial stream is generally warmer than the venous. The blood imparts heat to the air while passing through the lungs, and consequently the contents of the right side of the heart has a higher temperature than the contents on the left side.
24. What do we learn by means of the spectroscope? "Carriers of oxygen?" Blue blood in the system?
24. By means of the spectroscope, we learn that the change of color in the blood has its seat in the corpuscles; and that, according as they retain oxygen, or release it, they present the spectrum of arterial or venous blood. There evidently exists, on the part of these little bodies, an affinity for this gas, and hence they have been called "carriers of oxygen." It was long ago thought that blue blood was a trait peculiar to persons of princely and royal descent, and boastful allusions to the "sang azure" of kings and nobles are quite often met with. Physiology, however, informs us that blue blood flows in the veins of the low as well as the high, and that so far from its presence indicating a mark of purity, it, in reality, represents the waste and decay of the system.
25. The amount of air that passes in and out of the lungs?
25. Amount of Respiratory Labor.—During ordinary calm respiration, we breathe eighteen times in a minute; and twenty cubic inches of air pass in and out of the lungs with every breath. This is equivalent to the use of three hundred and sixty cubic inches, or more than ten pints of air each minute. From this we calculate that the quantity of air which hourly traverses the lungs is about thirteen cubic feet, or seventy-eight gallons; and daily, not less than three hundred cubic feet, an amount nearly equal to the contents of sixty barrels.
26. Air absorbed in its transit through the lungs? The loss? Carbonic acid exhaled? Effect of excitement or exertion? What estimate?
26. Of this large volume of air five per cent. is absorbed in its transit through the lungs. The loss thus sustained is almost wholly of oxygen, and amounts to fifteen cubic feet daily. The quantity of carbonic acid exhaled by the lungs during the day is somewhat less, being twelve cubic feet. Under the influence of excitement or exertion, the breathing becomes more frequent and more profound; and then the internal respiratory work increases proportionately, and may even be double that of the above estimate. It has been estimated that in drawing a full breath, a man exerts a muscular force equal to raising two hundred pounds placed upon the chest.
27. Importance of the oxygen in the atmosphere? Injurious character of gases?
27. Impurities of the Air.—The oxygen in the atmosphere is of such prime importance, and its proportion is so nicely adjusted to the wants of man, that any gas or volatile substance which supplants it must be regarded as a hurtful impurity. All gases, however, are not alike injurious. Some, if inhaled, are necessarily fatal; arsenuretted hydrogen being one of these, a single bubble of which destroyed the life of its discoverer, Gehlen. Others are not directly dangerous, but by taking the place of oxygen, and excluding it from the lungs, they become so. Into this latter class we place carbonic acid.
28. Pungency of gases? The inference? Our safeguard?
28. Most of the actively poisonous gases have a pungent or offensive odor; and, as may be inferred, most repugnant odors indicate the presence of substances unfit for respiration. Accordingly, as we cannot see or taste these impurities, the sense of smell is our principal safeguard against them; and we recognize the design which has planted this sense, like a sentinel at the proper entrance of the air-passages, the nostrils, to give us warning of approaching harm. Take, as an example, the ordinary illuminating gas of cities, from which so many accidents happen. How many more deaths would it cause if, when a leak occurs, we were not able to discover the escape of the gas by means of its disagreeable odor.
29. The air of rooms in which fever-sick persons are confined?
29. Organic matters exist in increased measure in the expired breath of sick persons, and impart to it, at times, a putrid odor. This is especially true in diseases which, like typhus and scarlet fever, are referable to a blood poison. In such cases the breath is one of the means by which nature seeks to expel the offending material from the system. Hence, those who visit or administer to fever-sick persons should obey the oft-repeated direction, "not to take the breath of the sick." At such times, if ever, fresh air is demanded, not alone for the sick, but as well for those who are in attendance.
30. Animalcula in the water? Dust in the air?
30. Dust in the Air.—Attention has lately been directed to the dust, or haze, that marks the ray of sunshine across a shaded room. Just as, many years ago, it was discovered that myriads of animalcula infested much of the water we drank, so now the microscope reveals "the gay motes that dance along a sunbeam" to be, in part, composed of multitudes of animal and vegetable forms of a very low grade, the germs of fermentation and putrefaction, and the probable sources of disease.
31. The best air filter? The remarks of Prof. Tyndall?
31. It is found that the best filter by which to separate this floating dust from the air is cotton wool, although a handkerchief will imperfectly answer the same purpose. In a lecture on this subject by Prof. Tyndall, he remarks that, "by breathing through a cotton wool respirator, the noxious air of the sick room is restored to practical purity. Thus filtered, attendants may breathe the air unharmed. In all probability, the protection of the lungs will be the protection of the whole system. For it is exceedingly probable that the germs which lodge in the air-passages are those which sow epidemic disease in the body. If this be so, then disease can certainly be warded off by filters of cotton wool. By this means, so far as the germs are concerned, the air of the highest Alps may be brought into the chamber of the invalid."
32. Carbonic acid in volcanic regions? In Java? At Lake Avernus? In mines?
32. Carbonic Acid in the Air.—We have already spoken of this gas as an exhalation from the lungs, and a source of impurity; but it exists naturally in the atmosphere in the proportion of one half part per thousand. In volcanic regions it is poured forth in enormous quantities from fissures in the earth's surface. Being heavier than air, it sometimes settles into caves and depressions in the surface. It is stated that in the island of Java, there is a place called the "Valley of Poison," where the ground is covered with the bones of birds, tigers, and other wild animals, which were suffocated by carbonic acid while passing. The Lake Avernus, the fabled entrance to the infernal regions, was, as its name implies, bird-less, because the birds, while flying over it, were poisoned by the gas and fell dead into its waters. In mines, carbonic acid forms the dreaded choke-damp, while carburetted hydrogen is the fire-damp.
33. In the open air? Amount of carbonic acid exhaled by a man? A gas-burner? A room fire? From furnaces?
33. In the open air, men seldom suffer from carbonic acid, for, as we shall see presently, nature provides for its rapid distribution, and even turns it to profitable use. But its ill effects are painfully evident in the abodes of men, in which it is liable to collect as the waste product of respiration and of that combustion which is necessary for lighting and warming our homes. A man exhales, during repose, not less than one-half cubic foot of carbonic acid per hour. One gas-burner liberates five cubic feet in the same time, and spoils about as much air as ten men. A fire burning in a grate or stove emits some gaseous impurity, and at the same time abstracts from the air as much oxygen as twelve men would consume in the same period, thus increasing the relative amount of carbonic acid in the air. From furnaces, as ordinarily constructed, this gas, with other products of combustion, is constantly leaking and vitiating the air of tightly-closed apartments.
34. Effects of inhaling carbonic acid alone? In small quantities?
34. Effects of Impure Air.—Carbonic acid, in its pure form, is irrespirable, causing rapid death by suffocation. Air containing forty parts per thousand of this gas (the composition of the expired breath) extinguishes a lighted candle, and is fatal to birds; when containing one hundred parts, it no longer yields oxygen to man and other warm-blooded animals; and is of course at once fatal to them. In smaller quantities, this gas causes headache, labored respiration, palpitation, unconsciousness, and convulsions.
35. Effects of the air in crowded and badly ventilated rooms?
35. In crowded and badly ventilated apartments, where the atmosphere relatively contains from six to ten times the natural amount of carbonic acid, the contaminated air causes dulness, drowsiness, and faintness; the dark, impure blood circulating through the brain, oppressing that organ and causing it to act like a blunted tool. This is a condition not uncommon in our schools, churches, court-rooms, and the like, the places of all others where it is desirable that the mind should be alert and free to act; but, unhappily, an unseen physiological cause is at work, dispensing weariness and stupor over juries, audience, and pupils.
36. A cause of consumption? How was the fact illustrated?
36. Another unmistakable result of living in and breathing foul air is found in certain diseases of the lungs, especially consumption. For many years the barracks of the British army were constructed without any regard to ventilation; and during those years the statistics showed that consumption was the cause of a very large proportion of deaths. At last the government began to improve the condition of the buildings, giving larger space and air-supply; and as a consequence, the mortality from consumption has diminished more than one-third.
37. How, in the case of the lower animals? Tendency of certain occupations?
37. The lower animals confined in the impure atmosphere of menageries, contract the same diseases as man. Those brought from a tropical climate, and requiring artificial warmth, generally die of consumption. In the Zoological gardens of Paris, this disease affected nearly all monkeys, until care was taken to introduce fresh air by ventilation; and then it almost wholly disappeared. The tendency of certain occupations to shorten life is well known; disease being occasioned by the fumes and dust which arise from the material employed, in addition to the unhealthful condition of the workshop or factory where many hours are passed daily.
38. Give the fact as set forth in the table.
38. The following table shows the comparative amount of carbonic acid in the air under different conditions and the effects sometimes produced:—
Proportion of Carbonic Acid. In 1000 parts of Air. Air of country. .4 " " city. .5 In hospital, well ventilated. .6 In school, church, etc., fairly ventilated. 1.2 to 2.5 In court-house, factory, etc., without ventilation. 4. to 40. In bedroom, before being aired. 4.5 In bedroom, after being aired. 1.5 Constantly breathed, causing ill health. 2. Occasionally breathed, causing discomfort. 3. Occasionally breathed, causing distress. 10. Expired air. 40. Air no longer yielding oxygen 100. 39. What can you state of the diffusive power of gases? The added influence of the winds?
39. Nature's Provision for Purifying the Air.—We have seen that carbonic acid is heavier than air, and is poisonous. Why, then, does it not sink upon and overwhelm mankind with a silent, invisible wave of death? Among the gases there is a more potent force than gravity, which forever precludes such a tragedy. It is known as the diffusive power of gases. It acts according to a definite law, and with a resistless energy compelling these gases, when in contact, to mingle until they are thoroughly diffused. The added influence of the winds is useful, by insuring more rapid changes in the air; air in motion being perfectly wholesome. The rains also wash the air.
40. How is the constant purity of the air secured? Explain the process?
40. We have seen that the whole animal creation is constantly abstracting oxygen from the atmosphere, and as constantly adding to it vast volumes of a gas injurious alike to all, even in small quantities. How, then, does the air retain, unchanged, its life-giving properties? The constant purity of the air is secured by means of the vegetable creation. Carbonic acid is the food of the plants, and oxygen is its waste product. The leaves are its lungs, and under the stimulus of sunlight a vegetable respiration is set in motion, the effects of which are just the reverse of the function we have been considering. Thus nature purifies the air, and at the same time builds up beautiful and useful forms of life from elements of decay.
41. What process occurs in the sea? How is the fact illustrated?
41. In the sea, as in the air, the same circle of changes is observed. Marine animals consume oxygen and give off carbonic acid; while marine plants consume carbonic acid and liberate oxygen. Taking advantage of this fact, we may so arrange aquaria with fishes and sea-plants, in their proper combinations, so that each supplies the needs of the other, and the water requires seldom to be renewed. This affords us, on a small scale, an illustration of the mutual dependence of the two great kingdoms of nature; as well as of those compensating changes which are taking place on such a grand scale in the world about us.
42. Character of the external air? Of the air in our dwellings? What becomes imperative? Imperfect ventilation of our dwellings?
42. Ventilation.—Since the external atmosphere, as provided by nature, is always pure, and since the air in our dwellings and other buildings is almost always impure, it becomes imperative that there should be a free communication from the one to the other. This we aim to accomplish by ventilation. As our houses are ordinarily constructed, the theory of ventilation, "to make the internal as pure as the external air," is seldom carried out. Doors, windows, and flues, the natural means of replenishing the air, are too often closed, almost hermetically, against the precious element. Special means, or special attention, must therefore be used to secure even a fair supply of fresh air. This is still more true of those places of public resort, where many persons are crowded together.
43. What hints are given for the ventilation of our dwellings?
43. If there are two openings in a room, one as a vent for foul air, and the other an inlet for atmospheric air, and if the openings be large, in proportion to the number of air consumers, the principal object will be attained. Thus, a door and window, each opening into the outer air, will ordinarily ventilate a small apartment; or a window alone will answer, if it be open both above and below, and the open space at each end be not less than one inch for each occupant of the room, when the window is about a yard wide. The direction of the current is generally from below upward, since the foul, heated air tends to rise; but this is not essential. Its rate need not be rapid; a "draught," or perceptible current, is never necessary to good ventilation. The temperature of the air admitted may be warm or cold. It is thought by many that if the air is cold, it is pure; but this is an error, since cold air will receive and retain the same impurities as warm air.
44. State what Florence Nightingale says about inhaling night air?
44. Shall we open our bedrooms to the night air? Florence Nightingale says, in effect, that night air is the only air that we can then breathe. "The choice is between pure air without and impure air within. Most people prefer the latter,—an unaccountable choice. An open window, most nights in the year, can hurt no one. In great cities, night air is the best and purest to be had in twenty-four hours. I could better understand, in towns, shutting the windows during the day than during the night."
45. Warmth of the bird as compared with that of the air? Of the fish and the water? Heat in animals and plants? How illustrated with the thermometer?
45. Animal Heat.—Intimately connected with respiration is the production of animal heat, or the power of maintaining the temperature of the body above that of the medium in which the creature moves; thus, the bird is warmer than the air, and the fish than the water. This elevation of temperature is a result of the various chemical changes which are constantly taking place in the system. Although common to all animals, in a greater or less degree, heat is not peculiar to them; since plants also generate it, especially at the time of sprouting and flowering. If a thermometer be placed in a cluster of geranium flowers, it will indicate a temperature several degrees above that of the surrounding air.
46. Amount of heat in animals, how apportioned? As regards the birds? Frogs, and other sluggish animals? Arrangement made by zoologists?
46. Among animals great differences are noticed in this respect, but the degree of heat produced is always proportional to the activity of respiration and the amount of oxygen consumed. Accordingly, the birds, whose habits are extremely active, and whose breathing capacity is the greatest, have uniformly the highest temperature. Sluggish animals, on the contrary, as frogs, lizards, and snakes, have little need for oxygen, and have incompletely developed lungs; these animals are cold to the touch, that is, they have relatively a lower temperature than man, and their positive temperature is but little above that of the external air. Accordingly, zoologists have so arranged the animal kingdom that warm-blooded animals, including man, the birds, and the quadrupeds, are classified together; while the cold-blooded animals, such as the fish, tortoise, frog, and all that have no vertebral column, are classed by themselves.
47. State what is said respecting the temperature of the human body.
47. The temperature of the human body is about 100° Fahrenheit, and remains about the same through winter and summer, in the tropics as well as in the frozen regions of the north. It may change temporarily within the range of about twelve degrees; but any considerable, or long-continued elevation or diminution of the bodily heat is certain to result disastrously.
| Venous Blood. | Arterial Blood. | |
| Color, | Dark blue, | Scarlet. |
| Oxygen, | 8 per cent., | 18 per cent. |
| Carbonic Acid, | 15 to 20 per cent., | 6 per cent., or less. |
| Water, | More, | Less. |
| Proportion of Carbonic Acid. | In 1000 parts of Air. |
| Air of country. | .4 |
| " " city. | .5 |
| In hospital, well ventilated. | .6 |
| In school, church, etc., fairly ventilated. | 1.2 to 2.5 |
| In court-house, factory, etc., without ventilation. | 4. to 40. |
| In bedroom, before being aired. | 4.5 |
| In bedroom, after being aired. | 1.5 |
| Constantly breathed, causing ill health. | 2. |
| Occasionally breathed, causing discomfort. | 3. |
| Occasionally breathed, causing distress. | 10. |
| Expired air. | 40. |
| Air no longer yielding oxygen | 100. |