processes, in part at least attributable to this factor, may justly be regarded as within the scope of this field; also an occasional sporadic diarrhea reasonably ascribed to a discharge of considerable numbers of streptococci or allied organisms from oral abscesses through the stomach into the intestines, may likewise fall within the province of this subject, although these are considered more properly from the viewpoint of pathology. The stomach under normal conditions is quite free from microorganisms. Conditions that lead to achlorhydria may and frequently do lead to lactic acid fermentation within the stomach, and partial occlusion. of the pylorus may lead to stagnation of the gastric contents and various local types of fermentation or putrefaction. The upper parts of the small intestine, which ordinarily exhibit a decided fluctuation in the amount of material, contain considerable numbers of bacteria at the height of duodenal digestion, and comparatively few organisms when the interdigestive period is reached. The greater part of the bacteria which appear during the digestive period are transported mechanically to lower levels with the duodenal contents. The actual number of types of bacteria found in the duodenal contents may appear to be considerable. Many appear to be swept into the duodenum from the stomach. The varieties which grow more luxuriantly in the duodenum, however, are relatively few in number. Their activities, depending somewhat upon the relative amounts of proteins and carbohy drates, are expended chiefly upon the sugars and upon the intermediate products of protein digestion, as the albumoses and peptones. Ordinarily the products formed appear to be comparatively small in amount and innocuous. The relatively feeble development of bacteria at this level, and the somewhat intermittent character of their growth due to the ebb and flow of food at this point, are in harmony with this view. Vincent and others have shown, however, that occlusion of a loop of intestine at this level may lead to the production of substances of unknown nature and origin, which are very poisonous for the organism under these conditions. At the lower levels of the small intestine, where the passage of food is more nearly continuous, bacterial development and bacterial activity in the chemical sense are decidedly greater than at the higher levels. The products formed are partly determined by the rapidity of passage of food to the level under consideration, a slow movement being attended by increased hydrolysis of proteins, fats and carbohydrates and a differential rate of absorption from the tract in favor of the latter substances. When the carbohydrate moiety is reduced to nil, the protein residue is vigorously attacked by the bacteria present, and a variety of products, among which indol, phenolic bodies as cresols and phenols, H2S and NH, and rarely products like beta-iminazolylethylamin, which even in very small amounts may have a material pressor effect upon blood pressure, may be found. It is worthy of note that these products of protein putrefaction are not produced when the normal intestinal flora at this level is growing in a medium containing carbohydrate. Bacterial activity in the alimentary canal is most intense in the cecum and ascending branch of the large intestine. The relatively slow movement of the feces, the abundance of unassimilated food, the accumulation of organisms from higher levels, and the relative absence of products of bacterial activity inimical to their unrestrained development, all tend to create conditions favoring luxuriant growth of these microbes. Here again the products formed depend in considerable measure upon the relative proportions of protein derivatives, fats and carbohydrates. If the former predominate, intense putrefactive changes, resulting in the formation of putrefaction products similar to those mentioned above, take place; if the latter are present, even in relatively small amounts, putrefactive activities are reduced to a minimum. The desiccation of the fecal mass as it passes through the lower levels of the large intestine causes a rather abrupt decrease in bacterial activity; the fecal mass as it is voided is estimated to be made up of nearly fifty per cent of bacteria. Probably over eighty per cent of these are either dead or so reduced in viability that they fail to develop in artificial media. It would be difficult indeed to prepare a detailed statement of the effects of various abnormal conditions in the intestinal tract upon the products of bacterial development in the intestinal contents. In general, diarrhea, hastening the passage of food, tends to flood the lower levels of the tract with bacteria from above, thus causing abnormal extension downwards of the activities of bacteria normally found in upper levels. (Diarrheas in the upper levels may not necessarily be accompanied by correspondingly rapid peristalsis at lower levels.) This rapidity of passage naturally tends to reduce somewhat the amount of bacterial activity at a given level, but the reduction is probably slight. Stasis of the intestinal contents, particularly above the ileocecal valve, usually causes an extension upwards of bacteria normally found at lower levels. This is probably due in part to the gradual digestion of the food by the intestinal enzymes at higher levels corresponding in actual hydrolytic cleavage to compounds normally found at lower levels. Those bacteria which are best adapted to the new conditions grow by extension to the upper layers of the tract where the dietary environment is most suited for their development. There is a decided tendency towards a differential loss of carbohydrate by assimilation under such conditions, because carbohydrates (of the sugar series at least) appear to be more quickly diffusible than protein derivatives. Under these conditions the differential accumulation of protein tends to increase the putrefactive products. Cathartics and so-called intestinal antiseptics do not appear to decrease the bacterial population materially except as they promote rapidity of peristalsis and consequent mechanical voiding of those organisms thus removed. The reduction is usually transient and may be followed by a greater bacterial proliferation. There is no sharp line of demarcation between a normal and an abnormal bacteriological flora in the alimentary canal. An overgrowth of normal flora leading in general to abnormal putrefaction or fermentation may cause as much discomfort or even danger to life as the purely exogenous infections. This phase of the problem, however, is beyond the scope of the subject under immediate discussion. REFERENCES 1. KENDALL, ARTHUR I. Unpublished observations. 123 2. 3. 4. and WALKER. J. Infect. Dis., 1915, xvii, 442. DAY and WALKER. J. Infect. Dis., 1914, 451. 5. ESCHERICH. Darmbakterien des Säuglings, Stuttgart, 1886. 6. BESSAU. Referred to in Tobler's Allgemeine Pathologie und Physiologie der Ernährung und des Stoffwechsels im Kindesalter. BIBLIOGRAPHY BIENSTOCK. Arch. f. Hyg., 1899, vol. xxxvi, p. 335. HEBLER. Untersuchungen über pathogene Anaëroben, Jena, 1908. JUNGANO ET DISTASO. Les Anaërobies, Paris, 1910. KENDALL. J. Biol. Chem., 1909, vol. vi, p. 499. Boston M. & S. J., 1910, vol. clxiii, p. 398. Ibid., 1911, vol. clxiv, p. 288. J. Am. M. Ass., 1911, vol. lvi, p. 1084. KENDALL. J. Med. Research, 1911, vol. xxiv, p. 411. DAY and WALKER. J. Am. Chem. Soc. and SMITH. Boston M. & S. J., 1911, vol. clxv, p. 306. METCHNIKOFF. Prolongation of Life, 1908. RAHE. J. Infect. Dis., 1914, vol. xv, p. 141. RETTGER. Centralb. f. Bakteriol., 1914, vol. lxiii, p. 362. CHAPTER IX GENERAL CLASSIFICATION OF FOODS Necessity of Nitrogenous Foods: Nitrogen Cycle; Plants, Animals, Man, Definition of Food. Working Basis of Classification: Inorganic-Water, Salts; Organic- Foodstuffs: Combinations; Chief Elements; Accessory Substances― Man is an omnivorous animal, deriving his food from both the animal and vegetable kingdoms. The elements of all foods are derived from the inorganic earth, air and water, and every quarter of the globe contributes its portion to the food of civilized man. Nitrogenous Foods. The elements which enter into the composition of the human body are precisely the same as those which compose the structure of the lower animals and the various plants of the vegetable kingdom. Like all other animals, human beings are unable to assimilate these elements in their inorganic condition, and therefore the principal elements must be organized before they can be of use to the body as a food. This is brought about through the animals which derive their sustenance from the vegetables which they consume; the vegetables, in turn, derive them at first hand from the earth, air and water. This is a law of nature. Nitrogen chemically pure cannot be assimilated by animals. They must obtain this important and indispensable element of life through the vegetable kingdom either directly or indirectly, for there is no other possible way to obtain it in a form ready for assimilation. We are therefore at the mercy of the vegetable kingdom for our supply of nitrogen, without which life in any form is impossible. The amount of nitrogen required daily by an adult varies according to circumstances, but it averages about 300 grains. The mechanism of the human economy undergoes unceasing changes, owing to wear and repair of the structures which consist mainly of nitrogenous elements; so constantly is this change going on that no part of the body remains |