FOOTNOTES:
[43] When a 1.50% decoction is desired, use 2 rounded teaspoonfuls to the pint of water. “Diseases of Nutrition and Infant Feeding,” p. 222, by Morse and Talbot.
[44] “Beef juice is not the same as ‘dish gravy,’ since the latter contains a large amount of cooked fat and is often highly indigestible.” Morse and Talbot’s “Diseases of Nutrition and Infant Feeding.”
[45] Formula suggested by Finkelstein and Meyer.
[46] “Diet in Disease,” by Freidenwald and Ruhräh and other sources.
[47] Formulas marked with one star are those used in the Presbyterian Hospital, Chicago, Ill. Courtesy of Miss R. Straka, Dietitian. Formulas marked with two stars are used in the Olmsted Hospital, Mayo Clinic, Rochester, Minn. Courtesy of Misses Foley and Ellithorpe, Dietitians. Formulas unmarked are used by the author in Memphis General and St. Joseph’s Hospitals, Memphis, Tenn.
[48] “Treatment of Diabetes,” p. 538, by Joslin.
[49] “The Treatment of Diabetes Mellitus,” p. 531, by Joslin.
[50] “Starvation Treatment of Diabetes,” p. 43, by Hill and Eckman.
SECTION III
THE HUMAN MACHINE
CHAPTER VII
THE HUMAN BODY
Chemical Composition of the Body.—It has been estimated by various writers that the human body has an approximate average chemical composition[51] of—
| Oxygen | about 65.000 per cent | |
| Carbon | about 18.000 per cent | |
| Hydrogen | about 10.000 per cent | |
| Nitrogen | about 03.000 per cent | |
| Calcium | about 02.000 per cent | |
| Phosphorus | about 01.000 per cent | |
| Potassium | about 00.350 per cent | |
| Sulphur | about 00.250 per cent | |
| Sodium | about 00.150 per cent | |
| Chlorine | about 00.150 per cent | |
| Magnesium | about 00.050 per cent | |
| Iron | about 00.004 per cent | |
| Iodine | ||
| Fluorine | very minute quantities | |
| Silicon | ||
Dependence of the body upon Food.—The human body, like any other piece of machinery, undergoes a constant wear and tear incidental to the work it performs, but in the human machine this is not all that must be included in its upkeep. The replacing of the dead and cast out cells with new ones, the repairing of the worn cells, the furnishing of heat, not only for the running of the engine but for the maintenance of the body temperature,—all of these must be considered and cared for if life is to continue. In man-made machinery, the renewal of the worn parts, and the replacing of those no longer useful must be accomplished by an outside agency. But in the body this work is performed by the organism; and the material used for the purpose, as well as that which is used to furnish the heat necessary for the internal and external activities of the body is food.
Exceptions to this Rule.—Under normal conditions the body never uses its own structure either for fuel or to replace tissue losses. In starvation the body rebuilds its important tissues, such as the nerves and glands, at the expense of the less important ones, such as the connective tissues and the skeletal muscles (Taylor).
Science has proved that for the most part the body does not use the food materials in their original form, but carries them through a series of transformations into substances more easily handled by the organism.
Roughly speaking, we may say that the body carries the foodstuffs through practically four processes on the pathway through the body, namely, digestion, absorption, metabolism, elimination.
Processes Included in Digestion.—There are several processes concerned in this transformation of the food materials. Some are purely mechanical and have to do with the movement of the food mass through the digestive tract: others are of a chemical character and bring about distinct changes in the food materials themselves. These mechanical and chemical processes with the retarding and stimulating agents that influence them are called digestion.
Absorption.—After the food materials have undergone digestion, or simplification into more available substances, these substances are absorbed, that is, they are passed through the membranes lining the walls of the intestinal tract, and thence to the blood.
Metabolism.—The utilization of the transformed food materials and their final fate in the human body is included under the term Metabolism.
Elimination.—After the food materials have been utilized to the extent of the body’s ability to handle them, their waste products are cast out of the organism by way of the skin, the lungs, the intestines and the kidneys.
A brief description of these processes seems desirable here.
Digestion.—Mechanical digestion begins in the mouth, where through the action of the teeth, the tongue and the muscles of the jaw, the food material is ground up and liquefied to a certain extent and made ready for the chemical action which takes place, to a limited degree only, as a result of the salivary enzyme in the mouth. The eating of food causes a flow of saliva from the three pairs of large salivary glands, and from the numerous secretory cells situated in the membranes of the mouth. As a rule the food stays for too short a time in this organ for any appreciable amount of chemical action to take place, but the liquefaction of the food mass with the salivary juices which contain the ferment (ptyalin), prepares for its passage into the gastric organ, and allows the digestion of the starch (the only foodstuff affected by salivary digestant), to continue in that part of the stomach until its action is checked by the hydrochloric acid in the gastric juice.
Arrangement of Food in the Stomach.—To simplify the study of the gastric organs it may be well to think of the stomach as being divided into three regions, i.e., “the fundus, the middle region, and the pyloric end,”[52] each of which differs slightly from the other. After being swallowed, the food enters the region situated at the cardiac end, known as the fundus.
Motor Processes in the Stomach.—There are no peristaltic waves in the fundus of the stomach, and the movement of the food mass is accomplished through the stretching and contraction of the muscular walls of the organ which tends to churn and further mix it with the salivary juices as it is gently pushed out into the middle region. In this region the peristaltic waves begin and travel toward the pylorus and increase in force as digestion progresses, ceasing only with the emptying of the organ. When the first stratum of food reaches the middle of the stomach it is caught by these oscillating peristaltic waves and forced forward through the pyloric region and against the pylorus, from whence it is returned back through rings of constriction. This forward and backward movement continues as long as there is food in the stomach, thus thoroughly mixing the mass with the gastric juice and allowing the enzymes existing in the juices to have an opportunity for action (chemical digestion).
Passage of Food from Stomach.—The material prepared in the stomach, known as chyme, is passed into the duodenum through the pylorus. The opening of this sphincter is controlled, according to Cannon, to a certain extent by the liquefication of the chyme, but more especially by the presence of free acid in the stomach side of the pyloric orifice.
Behavior of Food in the Intestines.—The food does not pass at once along the canal, but waits in the duodenum until several portions have passed through. As the food mass is made alkaline in the presence of the intestinal juices, the pyloric valve closes, opening again as the contents nearest it on the stomach side are acidified.
Intestinal Movements.—The peristaltic waves in the small intestines begin in the upper part and start a course ever downward. These waves in the intestines are two-fold in character; the quick shallow wave which forces the food string forward, breaking it up into segments, and backward joining the segments together again, and the strong deep wave which carries the entire mass forward after each segmentation. This method of movement in the small intestines is the best one possible under the conditions which prevail in this region of the digestional apparatus, since it not only mixes the food material with the juices necessary for its digestion, but likewise spreads it out over a wide space, insuring a greater contact with the absorbing walls of the small intestines.
The Effect of Muscular Constrictions.—The muscular constrictions occurring in the intestines producing segmentation of the food string have, according to Sherman, the effect of “(1) further mixing of the food and digestive juices, (2) bringing the digested food into contact with the absorbing membrane, (3) emptying the venous and lymphatic radicles in the membrane, the material which they have absorbed being forced into the veins and lymph vessels by the compression of the intestinal walls.”[53]
Movements in the Large Intestine.—The movements in the large intestine or colon are much like those in other parts of the digestive tract. The small and large intestine are divided by a valve known as the ileocecal valve, and any food which passes through it cannot return, since the valve is a competent one. The cells in the walls of the larger intestine secrete fluids of a lubricating character, containing no enzymes of digestion but aiding in moving the fecal matter toward the rectum.
Distribution of Secretory Cells.—Secretory cells are distributed in each of the three regions of the stomach, but are more numerous in the middle region than at either end. The third region includes the pyloric vestibule through which all foods must pass before they can enter the small intestine, and terminates in the pylorus, the valve which shuts off the stomach from the duodenum and the rest of the intestinal canal.
Chemical Digestion.—The chemical changes in the food materials, after they are eaten, are brought about through the action of certain substances known as soluble ferments or “enzymes.” These enzymes exist in every tissue of the body, and their province is first to break down the food materials themselves into simpler compounds, and then to reconstruct the simpler substances into those of a more complex character, which are more available for the various uses of the organism.
Action of the Enzymes.—As Sherman has stated, “all fermentation is brought about either directly or indirectly by the activity of animal or vegetable organisms or cells. When the organisms or cells act directly and the chemical changes occur only in their presence, the fermentation is said to be due to an organized ferment. When the action is not brought about directly by the cell itself, but by means of a substance secreted by the cell but acting apart from it, this substance is called a soluble or unorganized ferment or ‘enzyme.’” The enzymes concerned in digestion and metabolism, their source and their action, may be found in the following table:
TABLE OF ENZYMES[54]
Source and Action of Enzymes
| Enzymes | Where chiefly found | Action | |||
| Act upon carbohydrates | Ptyalin (salivary amylase) | Salivary secretions | Converts starch to maltose | ||
| Amylopsin (pancreatic amylase) | Pancreatic juice | Converts starch to maltose | |||
| Liver diastase | Liver | Converts glycogen to glucose | |||
| Muscle diastase | Muscles | Converts glycogen to glucose | |||
| Invertase (sucrase) | Intestinal juice | Converts glycogen to glucose and fructose | |||
| Maltase | Intestinal juice | Converts maltose to glucose | |||
| Lactase | Intestinal juice | Converts lactose to glucose and galactose | |||
| Glycolytic enzymes | Muscles, etc. | Split and oxidize glucose | |||
| Acts on fats | Lipase (steapsin) | Gastric, and pancreatic secretions, blood and tissues | Splits fats to fatty acids and glycerin | ||
| Act on proteins | Pepsin | Gastric juice | Splits proteins to proteoses and peptones | ||
| Trypsin | Pancreatic juice | Splits proteins to proteoses, peptones, polypeptids and amino acids | |||
| Erepsin | Intestinal juice | Splits peptones to amino acids and ammonia | |||
| Autolytic enzymes | Tissue generally | Split body proteins to simpler substances | |||
| Act on purins | Guanase | Thymus, adrenals, pancreas | Changes guanin to xanthin | ||
| Adenase | Spleen, pancreas, liver | Changes adenin to hypoxanthin | |||
| Oxidases | Lungs, liver, muscles, etc. | Changes hypoxanthin to xanthin and to uric acid | |||
Classification of Enzymes.—Sherman classifies the enzymes of the body according to their effects:
1. The hydrolytic enzymes:
(a) Proteolytic or protein-splitting enzymes.
(b) Lipolytic or fat-splitting enzymes.
(c) Amylolytic or starch-splitting enzymes.
(d) Sugar-splitting enzymes.
2. The coagulating enzymes, such as thrombin or thrombase (the fibrin ferment) and rennin, which causes the clotting of milk.
3. The oxidizing enzymes or oxidases (which, if the oxidation be accompanied by a splitting off of amino groups, may be called “deaminizing” enzymes).
4. The reducing enzymes or “reductases.”
5. Those which produce carbon dioxide without the use of free “deamidizing” oxygen, such as zymase of yeast.
6. Enzymes causing the breaking down of a larger into a smaller molecule of the same composition, as in the production of lactic acid from glucose.