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 1 .".() grins, of fat, Zawilski 1 still found in the stomach 
974 grrns., in the intestine 6 - l!4 gnus.: 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 grins.), 
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 - 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 then absence in the faeces after the administra- 
tion of lecithin by the month ; as well as by the increase of phosphates 
in the urine after feeding on foods, such as volk of egg, rich in lecithin. 3 
BACTERIAL DIGESTIOK 
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, inadecpuate or wholly unsnited 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. tit. 2 Arch. f. Anat. u. Physiol., Leipzig, 1890, Supp. Bd., S. 116. 
3 A. Bokav, Ztschr. f. physiol. Chem., Strassburg, 1877, Bd. i. S. 157; see also Hase- 
broek, ibid., 1888, Bd.'xii. S. 148. 
4 See p. 364. 
