XX. DIGESTION AND ABSORPTION
Problems.—To determine where digestion takes place by examining:—
(a) The functions of glands.
(b) The work done in the mouth.
(c) The work done in the stomach.
(d) The work done in the small intestine.
(e) The function of the liver.
To discover the absorbing apparatus and how it is used.
Laboratory Suggestions
Demonstration of food tube of man (manikin).—Comparison with food tube of frog. Drawing (comparative) of food tube and digestive glands of frog and man.
Demonstration of simple gland.—(Microscopic preparation.)
Home experiment and laboratory demonstration.—The digestion of starch by saliva. Conditions favorable and unfavorable.
Demonstration experiment.—The digestion of proteins with artificial gastric juice. Conditions favorable and unfavorable.
Demonstration.—An emulsion as seen under the compound microscope.
Demonstration.—Emulsification of fats with artificial pancreatic fluid. Digestion of starch and protein with artificial pancreatic fluid.
Demonstration of "tripe" to show increase of surface of digestive tube.
Laboratory or home exercise.—Make a table showing the changes produced upon food substances by each digestive fluid, the reaction (acid or alkaline) of the fluid, when the fluid acts, and what results from its action.
Purpose of Digestion.—We have learned that starch and protein food of plants are formed in the leaves. A plant, however, is unable to make use of the food in this condition. Before it can be transported from one part of the plant body to another, it is changed into a soluble form. In this state it can be passed from cell to cell by the process of osmosis. Much the same condition exists in animals. In order that food may be of use to man, it must be changed into a state that will allow of its passage in a soluble form through the walls of the alimentary canal, or food tube. This is done by the enzymes which cause digestion. It will be the purpose of this chapter to discover where and how digestion takes place in our own body.
The digestive tract of the frog and man. Gul, gullet; S, stomach; L, liver; G, gall bladder; P, pancreas; Sp, spleen; SI, small intestine; LI, large intestine; V, appendix; A, anus.
Alimentary Canal.—In all vertebrate animals, including man, food is taken in the mouth and passed through a food tube in which it is digested. This tube is composed of different portions, named, respectively, as we pass from the mouth downward, the gullet, stomach, small and large intestine, and rectum.
Comparison of Food Tube of a Frog and Man.—If we compare the food tube of a dissected frog with the food tube of man (as shown by a manikin or chart), we find part for part they are much the same. But we notice that the intestines of man, both small and large, are relatively longer than in the frog. We also notice in man the body cavity or space in which the internal organs rest is divided in two parts by a wall of muscle, the diaphragm, which separates the heart and lungs from the other internal organs. In the frog no muscular diaphragm exists. In the frog we can see plainly the silvery transparent mesentery or double fold of the lining of the body cavity in which the organs of digestion are suspended. Numerous blood vessels can be found especially in the walls of the food tube.
Glands.—In addition to the alimentary canal proper, we find a number of digestive glands, varying in size and position, connected with the canal.
Diagram of a gland. i, the common tube which carries off the secretions formed in the cells lining the cavity c; a, arteries carrying blood to the glands; v, veins taking blood away from the glands.
What a Gland Does. Enzymes.—In man there are the saliva gland of the mouth, the gastric glands of the stomach, the pancreas and liver, the two latter connected with the small intestine, and the intestinal glands in the walls of the intestine. Besides glands which aid in digestion there are several others of which we will speak later. As we have already learned, a gland is a collection of cells which takes up material from within the body and manufactures from it something which is later poured out as a secretion. An example of a gland in plants is found in the nectar-secreting cells of a flower.
Certain substances, called enzymes, formed by glands cause the digestion of food. The enzymes secreted by the cells of the glands and poured out into the food tube act upon insoluble foods so as to change them to a soluble form. They are the product of the activity of the cell, although they are not themselves alive. We do not know much about enzymes themselves, but we can observe what they do. Some enzymes render soluble different foods, others work in the blood, still others probably act within any cell of the body as an aid to oxidation, when work is done. Enzymes are very sensitive to changes in temperature and to the degree of acidity or alkalinity[42] of the material in which they act. We will find that the enzymes found in glands in the mouth will not act long in the stomach because of the change from an alkaline surrounding in the mouth to that of an acid in the stomach. Enzymes seem to be able to work indefinitely, providing the surroundings are favorable. A small amount of digestive fluid, if it had long enough to work, could therefore digest an indefinite amount of food.
Gland Structure.—The entire inner surface of the food tube is covered with a soft lining of mucous membrane. This is always moist because certain cells, called mucus cells, empty out their contents into the food tube, thus lubricating its inner surface. When a large number of cells which have the power to secrete fluids are collected together, the surface of the food tube may become indented at this point to form a pitlike gland. Often such depressions are branched, thus giving a greater secreting surface, as is seen in the figure on page [298]. The cells of the gland are always supplied with blood vessels and nerves, for the secretions of the glands are under the control of the nervous system.
How a Gland Secretes.—We must therefore imagine that as the blood goes to the cells of a gland it there loses some substances which the gland cells take out and make over into the particular enzyme that they are called upon to manufacture. Under certain conditions, such as the sight or smell of food, or even the desire for it, the activity of the gland is stimulated. It then pours out its secretion containing the digestive enzyme. Thus a gland does its work.
Salivary Glands.—We are all familiar with the substance called saliva which acts as a lubricant in the mouth. Saliva is manufactured in the cells of three pairs of glands which empty into the mouth, and which are called, according to their position, the parotid (beside the ear), the submaxillary (under the jawbone), and the sublingual (under the tongue).
Digestion of Starch.—If we collect some saliva in a test tube, add to it a little starch paste, place the tube containing the mixture for a few minutes in tepid water, and then test with Fehling's solution, we shall find grape sugar present. Careful tests of the starch paste and of the saliva made separately will usually show no grape sugar in either.
Experiment showing non-osmosis of starch in tube A, and osmosis of sugar in tube B.
If another test be made for grape sugar, in a test tube containing starch paste, saliva, and a few drops of any weak acid, the starch will be found not to have changed. The digestion or change of starch to grape sugar is caused by the presence in the saliva of an enzyme, or digestive ferment. You will remember that starch in the growing corn grain was changed to grape sugar by an enzyme called diastase. Here a similar action is caused by an enzyme called ptyalin. This ferment acts only in an alkaline medium at about the temperature of the body.
The mouth cavity of man. e, Eustachian tube; hp, hard palate; sp, soft palate; ut, upper teeth; bc, buccal cavity; lt, lower teeth; t, tongue; ph, pharynx; ep, epiglottis; lx, voice box; oe, gullet; tr, trachea.
Mouth Cavity in Man.—In our study of a frog we find that the mouth cavity has two unpaired and four paired tubes leading from it. These are (a) the gullet or food tube, (b) the windpipe (in the frog opening through the glottis), (c) the paired nostril holes (posterior nares), (d) the paired Eustachian tubes, leading to the ear. All of these openings are found in man.
In man the mouth cavity, and all internal surfaces of the food tube, are lined with a mucous membrane. The mucus secreted from gland cells in this lining makes a slippery surface so that the food may slip down easily. The roof of the mouth is formed in front by a plate of bone called the hard palate, and a softer continuation to the back of the mouth, the soft palate. These separate the nose cavity from that of the mouth proper. The part of the space back of the soft palate is called the pharynx, or throat cavity. From the pharynx lead off the gullet and windpipe, the former back of the latter. The lower part of the mouth cavity is occupied by a muscular tongue. Examination of its surface with a looking-glass shows it to be almost covered in places by tiny projections called papillæ. These papillæ contain organs known as taste buds, the sensory endings of which determine the taste of substances. The tongue is used in moving food about in the mouth, and in starting it on its way to the gullet; it also plays an important part in speaking.
I. Teeth of the upper jaw, from below. 1, 2, incisors; 3, canine; 4, 5, premolars; 6, 7, 8, molars. II. longitudinal section of a tooth. E, enamel; D, dentine; C, cement; P, pulp cavity.
The Teeth.—In man the teeth, unlike those of the frog, are used in the mechanical preparation of the food for digestion. Instead of holding prey, they crush, grind, or tear food so that more surface may be given for the action of the digestive fluids. The teeth of man are divided, according to their functions, into four groups. In the center of both the upper and lower jaw in front are found eight teeth with chisel-like edges, four in each jaw; these are the incisors, or cutting teeth. Next is found a single tooth on each side (four in all); these have rather sharp points and are called the canines. Then come two teeth on each side, eight in all, called premolars. Lastly, the flat-top molars, or grinding teeth, of which there are six in each jaw. Food is caught between irregular projections on the surface of the molars and crushed to a pulpy mass.
Hygiene of the Mouth.—Food should simply be chewed and relished, with no thought of swallowing. There should be no more effort to prevent than to force swallowing. It will be found that if you attend only to the agreeable task of extracting the flavors of your food, Nature will take care of the swallowing, and this will become, like breathing, involuntary. The instinct by which most people eat is perverted through the "hurry habit" and the use of abnormal foods. Thorough mastication takes time, and therefore one must not feel hurried at meals if the best results are to be secured. The stopping point for eating should be at the earliest moment after one is really satisfied.
Care of the Teeth.—It has been recently found that fruit acids are very beneficial to the teeth. Vinegar diluted to about half strength with water makes an excellent dental wash. Clean your teeth carefully each morning and before going to bed. Use dental silk after meals. We must remember that the bacteria which cause decay of the teeth are washed down into the stomach and may do even more harm there than in the mouth.
How Food is Swallowed.—After food has been chewed and mixed with saliva, it is rolled into little balls and pushed by the tongue into such position that the muscles of the throat cavity may seize it and force it downward. Food, in order to reach the gullet from the mouth cavity, must pass over the opening into the windpipe. When food is in the course of being swallowed, the upper part of this tube forms a trapdoor over the opening. When this trapdoor is not closed, and food "goes down the wrong way," we choke, and the food is expelled by coughing.
Peristaltic waves on the gullet of man. (A bolus means little ball.)
The Gullet, or Esophagus.—Like the rest of the food tube the gullet is lined by soft and moist mucous membrane. The wall is made up of two sets of muscles,—the inside ones running around the tube; the outer layer of muscle taking a longitudinal course. After food leaves the mouth cavity, it gets beyond our direct control, and the muscles of the gullet, stimulated to activity by the presence of food in the tube, push the food down to the stomach by a series of contractions until it reaches the stomach. These wavelike movements (called peristaltic movements) are characteristic of other parts of the food tube, food being pushed along in the stomach and the small intestine by a series of slow-moving muscular waves. Peristaltic movement is caused by muscles which are not under voluntary nervous control, although anger, fear, or other unpleasant emotions have the effect of slowing them up or even stopping them entirely.
Stomach of Man.—The stomach is a pear-shaped organ capable of holding about three pints. The end opposite to the gullet, which empties into the small intestine, is provided with a ring of muscle forming a valve called the pylorus. There is also another ring of muscle guarding the entrance to the stomach.
Gastric Glands.—If we open the stomach of the frog, and remove its contents by carefully washing, its wall is seen to be thrown into folds internally. Between the folds in the stomach of man, as well as in the frog, are located a number of tiny pits. These form the mouths of the gastric glands, which pour into the stomach a secretion known as the gastric juice. The gastric glands are little tubes, the lining of which secretes the fluid. When we think of or see appetizing food, this secretion is given out in considerable quantity. The stomach, like the mouth, "waters" at the sight of food. Gastric juice is slightly acid in its chemical reaction, containing about .2 per cent free hydrochloric acid. It also contains two very important enzymes, one called pepsin, and another less important one called rennin.
Action of Gastric Juice.—If protein is treated with artificial gastric juice at the temperature of the body, it will be found to become swollen and then gradually to change to a substance which is soluble in water. This is like the action of the gastric juice upon proteins in the stomach.
The other enzyme of gastric juice, called rennin, curdles or coagulates a protein found in milk; after the milk is curdled, the pepsin is able to act upon it. "Junket" tablets, which contain rennin, are used in the kitchen to cause this change.
A peptic gland, from the stomach, very much magnified. A, central or chief cell, which makes pepsin; B, border cells, which make acid. (From Miller's Histology.)
The hydrochloric acid found in the gastric juice acts upon lime and some other salts taken into the stomach with food, changing them so that they may pass into the blood and eventually form the mineral part of bone or other tissue. The acid also has a decided antiseptic influence in preventing growth of bacteria which cause decay, and some of which might cause disease.
Movement of Walls of Stomach.—The stomach walls, provided with three layers of muscle which run in an oblique, circular, and longitudinal direction (taken from the inside outward), are well fitted for the constant churning of the food in that organ. Here, as elsewhere in the digestive tract, the muscles are involuntary, muscular action being under the control of the so-called sympathetic nervous system. Food material in the stomach makes several complete circuits during the process of digestion in that organ. Contrary to common belief, the greatest amount of food is digested after it leaves the stomach. But this organ keeps the food in it in almost constant motion for a considerable time, a meal of meat and vegetables remaining in the stomach for three or four hours. While movement is taking place, the gastric juice acts upon proteins, softening them, while the constant churning movement tends to separate the bits of food into finer particles. Ultimately the semifluid food, much of it still undigested, is allowed to pass in small amounts through the pyloric valve, into the small intestine. This is allowed by the relaxation of the ringlike muscles of the pylorus.
Experiments on Digestion in the Stomach.—Some very interesting experiments have recently been made by Professor Cannon of Harvard with reference to movements of the stomach contents. Cats were fed with material having in it bismuth, a harmless chemical that would be visible under the X-ray. It was found that shortly after food reached the stomach a series of waves began which sent the food toward the pyloric end of the stomach. If the cat was feeling happy and well, these contractions continued regularly, but if the cat was cross or bad tempered, the movements would stop. This shows the importance of cheerfulness at meals. Other experiments showed that food which was churned into a soft mass was only permitted to leave the stomach when it became thoroughly permeated by the gastric juice. It is the acid in the partly digested food that causes the stomach valve to open and allow its contents to escape little by little into the small intestine.
The partly digested food in the small intestine almost immediately comes in contact with fluids from two glands, the liver and pancreas. We shall first consider the function of the pancreas.
Position and Structure of the Pancreas.—The most important digestive gland in the human body is the pancreas. The gland is a rather diffuse structure; its duct empties by a common opening with the bile duct into the small intestine, a short distance below the pylorus. In internal structure, the pancreas resembles the salivary glands.
Appearance of milk under the microscope, showing the natural grouping of the fat globules. In the circle a single group is highly magnified. Milk is one form of an emulsion. (S. M. Babcock, Wis. Bul. No. 61.)
Work done by the Pancreas.—Starch paste added to artificial pancreatic fluid and kept at blood heat is soon changed to sugar. Protein, under the same conditions, is changed to a peptone. Fats, which so far have been unchanged except to be melted by the heat of the body, are changed by the action of the pancreas into a form which can pass through the walls of the food tube. If we test pancreatic fluid, we find it strongly alkaline in its reaction. If two test tubes, one containing olive oil and water, the other olive oil and a weak solution of caustic soda, an alkali, be shaken violently and then allowed to stand, the oil and water will quickly separate, while the oil, caustic soda, and water will remain for some time in a milky emulsion. If this emulsion be examined under the microscope, it will be found to be made of millions of little droplets of fat, floating in the liquid. The presence of the caustic soda helped the forming of the emulsion. Pancreatic fluid similarly emulsifies fats and changes them into soft soaps and fatty acids. Fat in this form may be absorbed. The process of this transformation is not well understood.
Conditions under which the Pancreas does its Work.—The secretion from this gland seems to be influenced by the overflow of acid material from the stomach. This acid, on striking the lining of the small intestine, causes the formation in its walls of a substance known as secretin. This secretin reaches the blood and seems to stimulate all the glands pouring fluid into the intestine to do more work. A pint or more of pancreatic fluid is secreted every day.
The Intestinal Fluid.—Three different pancreatic enzymes do the work of digestion, one acting on starch, another on protein, and a third on fats. It has been found that some of these enzymes will not do their work unless aided by the intestinal fluid, a secretion formed in glands in the walls of the small intestine. This fluid, though not much is known about it, is believed to play an important part in the digestion of all kinds of foods left undigested in the small intestine.
Liver.—The liver is the largest gland in the body. In man, it hangs just below the diaphragm, a little to the right side of the body. During life, its color is deep red. It is divided into three lobes, between two of which is found the gall bladder, a thin-walled sac which holds the bile, a secretion of the liver. Bile is a strongly alkaline fluid of greenish color. It reaches the intestine through the same opening as the pancreatic fluid. Almost one quart of bile is passed daily into the digestive canal. The color of bile is due to certain waste substances which come from the destruction of worn-out red corpuscles of the blood. This destruction takes place in the liver.
Diagram of a bit of the wall of the small intestine, greatly magnified, a, mouths of intestinal glands; b, villus cut lengthwise to show blood vessels and lacteal (in center); e, lacteal sending branches to other villi; i, intestinal glands; m, artery; v, vein; l, t, muscular coats of intestine wall.
Functions of Bile.—The action of bile is not very well known. It has the very important faculty of aiding the pancreatic fluid in digestion, though alone it has slight if any digestive power. Certain substances in the bile aid especially in the absorption of fats. Bile seems to be mostly a waste product from the blood and as such incidentally serves to keep the contents of the intestine in a more or less soft condition, thus preventing extreme constipation.
The Liver a Storehouse.—Perhaps the most important function of the liver is the formation within it of a material called glycogen, or animal starch. The liver is supplied by blood from two sources. The greater amount of blood received by the liver comes directly from the walls of the stomach and intestine to this organ. It normally contains about one fifth of all the blood in the body. This blood is very rich in food materials, and from it the cells of the liver take out sugars to form glycogen.[43] Glycogen is stored in the liver until such a time as a food is needed that can be quickly oxidized; then it is changed to sugar and carried off by the blood to the tissue which requires it, and there used for this purpose. Glycogen is also stored in the muscles, where it is oxidized to release energy when the muscles are exercised.
The Absorption of Digested Food into the Blood.—The object of digestion is to change foods from an insoluble to a soluble form. This has been seen in the study of the action of the various digestive fluids in the body, each of which is seen to aid in dissolving solid foods, changing them to a fluid, and, in case of the bile, actually assisting them to pass through the wall of the intestine. A small amount of digested food may be absorbed by the blood in the blood vessels of the walls of the stomach. Most of the absorption, however, takes place through the walls of the small intestine.
Structure of the Small Intestine.—The small intestine in man is a slender tube nearly twenty feet in length and about one inch in diameter. If the chief function of the small intestine is that of absorption, we must look for adaptations which increase the absorbing surface of the tube. This is gained in part by the inner surface of the tube being thrown into transverse folds which not only retard the rapidity with which food passes down the intestine, but also give more absorbing surface. But far more important for absorption are millions of little projections which cover the inner surface of the small intestine.
The Villi.—So numerous are these projections that the whole surface presents a velvety appearance. Collectively, these structures are called the villi (singular villus). They form the chief organs of absorption in the intestine, several thousand being distributed over every square inch of surface. By means of the folds and villi the small intestine is estimated to have an absorbing surface equal to twice that of the surface of the body. Between the villi are found the openings of the intestinal glands.
Internal Structure of a Villus.—The internal structure of a villus is best seen in a longitudinal section. We find the outer wall made up of a thin layer of cells, the epithelial layer. It is the duty of these cells to absorb the semifluid food from within the intestine. Underneath these cells lies a network of very tiny blood vessels, while inside of these, occupying the core of the villus, are found spaces which, because of their white appearance after absorption of fats, have been called lacteals. (See figure, page [307].[TN6])
Diagram to show how the nutrients reach the blood.
Absorption of Foods.—Let us now attempt to find out exactly how foods are passed from the intestines into the blood. Food substances in solution may be soaked up as a sponge would take up water, or they may pass by osmosis into the cells lining the villus. These cells break down the peptones into a substance that will pass into and become part of the blood. Once within the villus, the sugars and digested proteins pass through tiny blood vessels into the larger vessels comprising the portal circulation. These pass through the liver, where, as we have seen, sugar is taken from the blood and stored as glycogen. From the liver, the food within the blood is sent to the heart, from there is pumped to the lungs, from there returns to the heart, and is pumped to the tissues of the body. A large amount of water and some salts are also absorbed through the walls of the stomach and intestine as the food passes on its course. The fats in the form of soaps and fatty acids pass into the space in the center of the villus. Later they are changed into fats again, probably in certain groups of gland cells known as mesenteric glands, and eventually reach the blood by way of the thoracic duct without passing through the liver.
Large Intestine.—The large intestine has somewhat the same structure as the small intestine, except that it lacks the villi and has a greater diameter. Considerable absorption, however, takes place through its walls as the mass of food and refuse material is slowly pushed along by the muscles within its walls.
Vermiform Appendix.—At the point where the small intestine widens to form the large intestine, a baglike pouch is formed. From one side of this pouch is given off a small tube about four inches long, closed at the lower end. This tube, the rudiment of what is an important part of the food tube in the lower vertebrates, is called the vermiform appendix. It has come to have unpleasant notoriety in late years, as the site of serious inflammation.
Constipation.—In the large intestine live millions of bacteria, some of which make and give off poisonous substances known as toxins. These substances are easily absorbed through the walls of the large intestine, and, when they pass into the blood, cause headaches or sometimes serious trouble. Hence it follows that the lower bowel should be emptied of this matter as frequently as possible, at least once a day. Constipation is one of the most serious evils the American people have to deal with, and it is largely brought about by the artificial life which we lead, with its lack of exercise, fresh air, and sleep. Fruit with meals, especially at breakfast, plenty of water between meals and before breakfast, exercise, particularly of the abdominal muscles, and regular habits will all help to correct this evil.
Hygienic Habits of Eating; the Causes and Prevention of Dyspepsia.—From the contents of the foregoing chapter it is evident that the object of the process of digestion is to break up solid food so that it may be absorbed to form part of the blood. Any habits we may form of thoroughly chewing our food will evidently aid in this process. Undoubtedly much of the distress known as dyspepsia is due to too hasty meals with consequent lack of proper mastication of food. The message of Mr. Horace Fletcher in bringing before us the need of proper mastication of food and the attendant evils of overeating is one which we cannot afford to ignore. It is a good rule to go away from the table feeling a little hungry. Eating too much overtaxes the digestive organs and prevents their working to the best advantage. Still another cause of dyspepsia is eating when in a fatigued condition. It is always a good plan to rest a short time before eating, especially after any hard manual work. We have seen how great a part unpleasant emotions play in preventing peristaltic movements of the food tube. Conversely, pleasant conversation, laughter, and fun will help you to digest your meal. Eating between meals is condemned by physicians because it calls the blood to the digestive organs at a time when it should be more active in other parts of the body.
Effect of Alcohol on Digestion.—It is a well-known fact that alcohol extracts water from tissues with which it is in contact. This fact works much harm to the interior surface of the food tube, especially the walls of the stomach, which in the case of a hard drinker are likely to become irritated and much toughened. In very small amounts alcohol stimulates the secretion of the salivary and gastric glands, and thus appears to aid in digestion.
The following results of experiments on dogs, published in the American Journal of Physiology, Vol. I, Professor Chittenden of Yale University gives as "strictly comparable," because "they were carried out in succession on the same day." They show that alcohol retards rather than aids in digestion:—
| Number of Experiment | 1/16 Lb. Meat With Water | 1/16 Lb. Meat With Dilute Alcohol | |
|---|---|---|---|
| XVII | α 9:15 A.M. | Digested in 3 hours | |
| XVII | β 3:00 P.M. | Digested in 3:15 hours | |
| XVIII | α 8:30 A.M. | Digested in 2:30 hours | |
| XVIII | β 2:10 P.M. | Digested in 3:00 hours | |
| XIX | α 9:00 A.M. | Digested in 2:30 hours | |
| XIX | β 2:30 P.M. | Digested in 3:00 hours | |
| XX | α 9:15 A.M. | Digested in 2:45 hours | |
| XX | β 2:30 P.M. | Digested in 2:15 hours | |
| VI | α 9:15 A.M. | Digested in 3:45 hours | |
| VI | β 1:00 P.M. | Digested in 3:15 hours | |
| Average | 2:42 hours | 3:09 hours | |
As a result of his experiments, Professor Chittenden remarks: "We believe that the results obtained justify the conclusion that gastric digestion as a whole is not materially modified by the introduction of alcoholic fluids with the food. In other words, the unquestionable acceleration of gastric secretion which follows the ingestion of alcoholic beverages is, as a rule, counterbalanced by the inhibitory effect of the alcoholic fluids upon the chemical process of gastric digestion, with perhaps at times a tendency towards preponderance of inhibitory action." Others have come to the same or stronger conclusions as to the undesirable action of alcohol on digestion, as a result of their own experiments.
Effect of Alcohol on the Liver.—The effect of heavy drinking upon the liver is graphically shown in the following table prepared by the Scientific Temperance Federation of Boston, Mass.:—
Proportion of deaths from disease in a certain area due to alcohol. The black area shows deaths due to alcohol.[44]
"Alcoholic indulgence stands almost if not altogether in the front rank of the enemies to be combated in the battle for health."—Professor William T. Sedgwick.
[42] The teacher should explain the meaning of these terms.
[43] It is known that glycogen may be formed in the body from protein, and possibly from fatty foods.
[44] Does not include deaths from general alcoholic paralysis or other organic diseases due to alcohol. Liver cirrhosis due to alcohol conservatively estimated at 75 per cent of total cases.