| FACING PAGE | |
| Photograph of one of the athletes | [190] |
| Photograph of soldiers taken at the close of the experiment | [194] |
| Photograph of soldiers taken at the close of the experiment | [194] |
| Photograph of Fritz at the close of the experiment | [200] |
| Photographs of the dogs experimented with | |
| Subject No. 5 August 19, 1905 | |
| Subject No. 5 November 18, 1905 | |
| Subject No. 5 April 24, 1906 | |
| Subject No. 5 June 27, 1906 | |
| Subject No. 3 August 19, 1905 | |
| Subject No. 3 November 18, 1905 | |
| Subject No. 3 April 24, 1906 | |
| Subject No. 3 June 27, 1906 | |
| Subject No. 13 January 2, 1906 | |
| Subject No. 13 February 27,1906 | |
| Subject No. 13 April 24, 1906 | |
| Subject No. 13 June 19, 1906 | |
| Subject No. 15 January 2, 1906 | |
| Subject No. 15 February 27, 1906 | |
| Subject No. 15 April 24, 1906 | |
| Subject No. 15 June 19, 1906 | |
| Subject No. 20 January 2, 1906 | |
| Subject No. 20 February 27, 1906 | |
| Subject No. 20 April 24, 1906 | |
| Subject No. 20 June 19, 1906 | |
| Subject No. 17 January 2, 1906 | |
| Subject No. 17 February 27, 1906 | |
| Subject No. 17 April 24, 1906 | |
| Subject No. 17 June 27, 1906 |
THE NUTRITION OF MAN
CHAPTER I
FOODS AND THEIR DIGESTION
Topics: The purpose of nutrition. The food of man. Proteid foods. Carbohydrate foods. Fats. Food as fuel. Composition of foodstuffs. Availability of foods. Food as source of energy. Various factors in the nourishment of the body. Processes of digestion. Secretion of saliva. Function of saliva. Enzymes. Reversible action of enzymes. Specificity of enzymes. Mastication. Gastric secretion. Components of gastric juice. Action of gastric juice. Muscular movements of stomach. Time foods remain in stomach. Importance of stomach digestion. Processes of the small intestine. Secretion of pancreatic juice. Chemical changes in small intestine. Destruction of proteid food. Significance of the breaking down of proteid. Change of fatty foods and carbohydrates in intestine. Digestion practically complete at end of small intestine. Putrefaction held in check. Digestion a prelude to utilization of food.
One of the great mysteries of life is the power of growth, that harmonious development of composite organs and tissues from simple protoplasmic cells, with the ultimate formation of a complex organism with its orderly adjustment of structure and function. Equally mysterious is that wonderful power of rehabilitation by which the cells of the body are able to renew their living substance and to maintain their ceaseless activity through a period, it may be of fourscore years, before succumbing to the inevitable fate that awaits all organic structures. This bodily activity, visible and invisible, is the result of a third mysterious process, more or less continuous as long as life endures, of chemical disintegration, decomposition, and oxidation, by which arises the evolution of energy to maintain the heat of the body and the power for mental and physical work.
These three main functions constitute the purpose of nutrition. The growth of the adult man from the tiny cell or germ that marks his simple beginning is at the expense of the food material he absorbs and assimilates. The rehabilitation of the cells, or the composite tissues of the fully developed organism, is accomplished through utilization of the daily food, whereby cell substance is renewed and all losses made good. The energy which manifests itself in the form of heat and mechanical or mental work, i. e., the energy by which the vital machinery is maintained in ceaseless activity, comes from the breaking down of the food materials by means of which, as the saying goes, the body is nourished. The body thus becomes the centre of different lines of activity, the food serving as the material out of which new cells and tissues are constructed, old cells revivified, and energy for running the bodily machinery derived. Development, growth, and vital activity all depend upon the availability of food in proper amounts and proper quality.
The food of man is composed mainly of organic materials, for while, as Dr. Curtis[1] has expressed it, “the plant can make organic matter out of inorganic elements, just this the animal cannot do at all. The thing of legs and locomotion, of spine and speech, can build his organic walls only out of organic bricks ruthlessly ripped from existing walls of other animals or plants.” It is true that man has need of certain inorganic salts in his daily diet, but they are in the nature of aids to nutrition (aside from such as are necessary for the formation of bone and teeth), contributing in some measure toward regulation and control of nutritive processes rather than as a source of energy to the body. Inorganic substances, however, are an integral part of the essential tissues and organs of the body, being combined with the organic constituents of the living cells. Indeed, electrolytes are perhaps the substances that put life into the proteids of the protoplasm, and it is truly important for the integrity and functional power of living cells that the proportion of inorganic constituents therein be kept in a constant condition of quality and quantity. Still, the food of mankind is essentially organic in nature, and while it may be exceedingly varied in character, ranging from the simple vegetable dietary of the natives of India and the Far East to the voluminous admixture of varied forms of animal and vegetable foodstuffs so acceptable to the bon vivant of our western civilization, the principles contained therein are few in number.
The organic foodstuffs are of three distinct types and are classified under three heads, viz.: Proteids or Albuminous foodstuffs, Carbohydrates, and Fats. All animal and vegetable foods, whatever their nature and whatever their origin, are composed simply of representatives of one or more of these three classes of food principles.
Proteid substances are characterized by containing about 16 per cent of nitrogen. In addition, they contain on an average 52 per cent of carbon, 7 per cent of hydrogen, 23 per cent of oxygen, and 0.5–2.0 per cent of sulphur. A certain class of proteids, known as nucleoproteids because of their occurrence in the nuclei of cells, contain likewise a small amount of phosphorus in organic combination. Proteid or albuminous substances constitute the chemical basis of all living cells, whether animal or vegetable. This means, expressed in different language, that the organic substance of all organs and tissues, whether of animals or plants, is made up principally of proteid matter. Proteid substances occupy, therefore, a peculiar position in the nutrition of man and of animals in general. They constitute the class of essential foodstuffs without which life is impossible. For tissue-building and for the renewal of tissues and organs, or their component cells, proteid or albuminous foodstuffs are an absolute requirement. The vital part of all tissue is proteid, and only proteid food can serve for its growth or renewal. Hence, no matter how generous the supply of carbohydrates and fats, without some admixture of proteid food the body will weaken and undergo “nitrogen starvation.” It is to be noted, however, that while the element nitrogen (16 per cent) gives character to the proteid or albuminous foodstuffs, so that they are frequently spoken of or classified as the “nitrogenous foodstuffs,” it is not the nitrogen per se that is so essential for the nutrition of the body. Man lives in an atmosphere of oxygen and nitrogen. He can and does absorb and utilize the free oxygen of the air he breathes; indeed, it is absolutely essential for his existence, but the free nitrogen likewise drawn into the lungs at each inspiration is of no avail for the needs of the body. Further, there are many compounds of nitrogen, some of them closely allied to the proteid foodstuffs in chemical composition, which are just as useless as free nitrogen in meeting the wants of the body for nitrogenous foods.