464 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
slight extent lactic fermentation. 1 A certain amount of decomposition 
of neutral fats also occurs during gastric digestion, yielding fatty acids, 
but it is not certainly known whether this is due to bacterial action or 
not. 2 
Intestinal bacterial digestion — Reaction of the intestine. — There 
is considerable difference of opinion both as to the amount of decom- 
position of foodstuffs due to bacterial action which goes on in the 
intestine, and as to the importance of such a decomposition as a normal 
factor in digestion. 
The extent of bacterial action can evidently be more accurately 
gauged by the amount of bacterial decomposition products formed than 
by the presence in the intestine of bacteria, which may not there be in 
a very active condition. 
Judged by this standard, the amount of proteid decomposition due 
to bacteria which takes place in the small intestine is excessively small, 
while a considerable amount takes place in the caecum and large intes- 
tine generally. When carbohydrates and proteids are present in the 
sn me solution along with various bacteria capable of attacking them, 
the carbohydrates are first attacked, the action being accompanied by 
the formation of certain organic acids ; at a later stage the proteids are 
attacked and decomposed. This has been shown by Maly, 3 who took 
mucous membrane of the stomach, placed it in a solution of cane-sugar, 
and kept the mixture at body temperature for several days. The lactic 
acid formed by the decomposition of the sugar was neutralised from 
time to time, and it was found that the process continued without a 
trace of putrefaction appearing, until all the sugar had been converted 
into lactate; then first appeared, often somewhat suddenly, an intense 
putrefactive odour, and the proteids began to be decomposed. 
It is probable from this that, in the body, bacterial action mi carbo- 
hydrates precedes that on proteids ; and it has been supposed by some 
that such an action commences with considerable intensity in the 
duodenum, and persists throughout the entire length of the small 
intestine, so involving bacterial decomposition of a large share of the 
carb< (hydrate food. 
This opinion rests chiefly on the observation that the acid reaction 
of the chyme in the stomach, due to hydrochloric acid, becomes replaced 
by an acid reaction, due to organic acids, in the small intestine. These 
organic acids are supposed to be set free by the action of certain bacteria, 
found in the small intestine, upon the carbohydrate food. 
Such a result has been obtained by Macfadyen, Xencki, and Sieber, 4 from 
observations made on a case of anus praeternaturalis in man, in which the 
fistula occurred quite at the lower end of the ileum. The intestinal contents 
arising from a mixed diet, consisting principally of animal food, had as they 
flowed from the fistula an acid reaction, equivalent to that of a solution of 
1 per mille of acetic acid; this reaction was principally due to acetic acid, 
1 In tins process hydrogen gas is set free along with lactic and traces of other acids ; 
under abnormal conditions the amount of gas may be greatly increased. See E. Wissel, 
Ztschr. f. physiol. Chem., Strassburg, 1895, Bd. xxi. S. 234, where the literature of this 
subject up to that date is given. 
2 Marcet, Proc. Roy. Soc. London, 1S58, vol. ix. p. 30(5 ; Cash, Arch. f. A nut. u. 
Physiol., Leipzig, 1880, S. 323. 
3 Hermann's "Handbueh," Bd. v. (2), S. 239. 
4 Arch. f. exper. Path. u. PharinahJ.. Leipzig, 1891, Bd. xxviii. S. 311, reprinted in Journ. 
Anal, and Physiol., London, 1S91, vol. xxv. p. 390. See also C. A. Ewald, Virchow 's Archiv, 
1879, Bd. lxxv. S. 409; and Jakowski. Arch. d. sc. biol., St. Petersbourg, 1892, tome i. p. 539. 
