BACTERIAL DIGESTION. 463 



After a full meal of fat, absorption, in the case of the dog, goes on 

 for about thirty hours. At the height of absorption, the chyle in the 

 thoracic duct may contain as much as 15 per cent, of fat. Twenty-one 

 hours after a meal of 150 grms. of fat, Zawilski * still found in the stomach 

 974 grms., in the intestine 6 '24 grms. ; in thirty hours all but traces 

 have disappeared from both stomach and intestine. Throughout this 

 period of digestion, according to the same observer, the amount of fat in 

 the intestine at any time remains practically constant (6'24 to 9'9 grms.), 

 from which it would seem that the rate at which the fat is allowed to 

 pass the pylorus is regulated by the amount of fat already present in the 

 intestine. 



None of the soap which may be formed during fat digestion and 

 absorption probably ever enters the general circulation as such, but is 

 reconverted into neutral fat beforehand; as Munk 2 has shown, soaps 

 of the alkalies intravenously injected produce poisonous effects, closely 

 resembling those obtained on injection of albumoses. 



As might be expected from their similar chemical constitution, the 

 lecithins are decomposed in the same manner as the fats by the steapsin 

 of the pancreatic juice, the products of the reaction being glycero- 

 phosphoric acid, neurin, and fatty acids. These products are probably 

 absorbed, as is shown by their absence in the fseces after the administra- 

 tion of lecithin by the mouth ; as well as by the increase of phosphates 

 in the urine after feeding on foods, such as yolk of egg, rich in lecithin. 3 



BACTERIAL DIGESTION. 



The food in the alimentary canal is acted upon, not only by the 

 digestive secretions and their enzymes, but to a greater or less extent by 

 certain bacteria which are never entirely absent, although the amount of 

 their action varies greatly, under healthy conditions, with the nature of the 

 food and the class of animal. Under abnormal conditions the growth of 

 these organisms may be greatly increased, and nutrition be seriously 

 impaired, by their turning to their own uses the products of normal 

 digestion, and leaving only for the service of the animal, degradation- 

 products, inadequate or wholly unsuited for the purposes of its meta- 

 bolism. Along with this increased growth of the bacteria normally 

 present in the stomach, conditions may become so changed as to favour 

 the growth of other bacteria, often pathogenic in character, which find 

 under normal conditions no favourable soil for their growth in the 

 intestinal contents, and thus various forms of disease may be introduced. 

 We have here, however, only to deal with the changes induced by 

 bacteria under a normal condition of the alimentary canal. 



In dealing with the function of the free hydrochloric acid of the 

 gastric juice, it has already been stated that this completely stops all 

 bacterial action, 4 so that it is only in the first stage of gastric secretion, 

 before the acidity has become marked, that any bacterial changes can occur. 



Proteids are not attacked during this first short stage (twenty to 

 forty minutes) of gastric digestion, but carbohydrates undergo to a 



1 Loc. (At. 2 Arch.f. Anat. u. PhysioL, Leipzig, 1890, Snpp. Bd., S. 116. 



3 A. Bokay, Ztschr. /. physiol. Chem., Strassburg, 1877, Bd. i. S. 157; see also Hase- 

 broek, ibid., 1888, Bd. xii. S. 148, 



4 See p. 364. 



