ACTION OF INTESTIN. iL BACTERIA ON PROTEIDS. t 465 
accompanied by traces of fermentation and paralactie acid, volatile fatty acids, 
succinic acid, and bile acids. Hydrochloric acid was no! present. The 
mixture had very little odour ; occasionally the slight odour it had was faintly 
putrefactive, resembling indol, but usually it was more like that of volatile 
fatty acids. These authors state that it is the organic acids present in the 
small intestine which limit the bacterial decomposition of carbohydrates, and 
prevent the putrefaction of proteids. 
On the other hand, Moore and Rockwood 1 state that the reaction of the 
intestine in various classes of animals (dog, cat, white rat, guinea-pig, and 
rabbit) is not normally acid throughout its entire length, and that the 
alkalinity increases in passing down the intestine. 
The presence of fat in the food causes in carnivora an acid reaction, which 
persists until the lower third of the intestine is reached. This acid reaction is 
due to very weak organic acid, most probably to the acids of the fats dissolved 
by the agency of the bile. 2 The alkalinhvv is much greater in herbivora than 
in carnivora, although herbivora consume much more carbohydrate food than 
carnivora. Also, in carnivora, the alkalinity is markedly increased by carbo- 
hydrate food ; this would not be the case if any considerable bacterial 
decomposition of carbohydrates took place in the small intestine, but the 
alkalinity would diminish from increased formation of organic acids. It is 
therefore probable that in these animals any extensive bacterial decomposition 
of carbohydrates that may occur, like that of proteids, takes place in the 
large intestine, and by analogy the same is probably the case in the human 
intestine. 
Considerable importance lias been attached to the normal action of bacteria 
in the intestine, and it has even been supposed that the presence of bacteria 
is essential to life. Such a view has recently been shown to be erroneous by 
an elaborate and painstaking research carried out by JSuttall and Thierfelder, 3 
who obtained ripe foetal guinea-pigs, by means of a Caesarean section, carried 
out under strict antiseptic precautions. They introduced the animals immedi- 
ately into an aseptic chamber, through which a current of filtered air was 
aspirated, and fed them hourly on sterilised milk day and night for over eight 
days. 
The animals lived and throve, and increased as much in weight as healthy 
normal animals, subjected to a similar diet for the purpose of controlling the 
results. Microscopic examination at the end of the experiment showed that 
the alimentary canal contained no bacteria of any kind, nor could cultures of 
any kind be obtained from it. The same authors, in a subsequent paper, 
describe the extension of their research to vegetable food ; this was also digested 
in the absence of bacteria. Under such conditions cellulose was not attacked ; 
hence they consider that the chief function of this material is to give bulk and 
a proper consistency to the food, so as to suit the conditions of herbivorous 
digestion. 
Action of the intestinal bacteria on proteids. — The changes brought 
about in the intestine are very similar and probably identical with those 
which occur when proteids undergo putrefaction in the air, with this 
important exception, that those putrefactive bacteria which produce the 
class of poisonous nitrogenous (alkaloidal) bases known as ptomaines do 
not grow under normal conditions in the intestine. This may be due to 
the intestinal contents not furnishing a suitable medium for their growth, 
or to the time of putrefaction in the intestine not being sufficiently 
prolonged. Ptomaines, and especially poisonous ones, are formed only in 
1 Journ. Physiol., Cambridge and London, 1897, vol. xxi. p. 373. 
2 See "Digestion and Absorption of Fats," p. 454. 
s Ztechr. f. physiol. Chem., Strassburg, 1895, Bd. xxi. S. 109; 1896, Bd. xxii. S. 62. 
VOL. I. 30 
