ACTION OF INTESTINAL BACTERIA ON PROTEIDS. 465 



accompanied by traces of fermentation and paralactic acid, volatile fatty acids, 

 succinic acid, and bile acids. Hydrochloric acid was not 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 Kockwood l 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 alkalinity 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 has 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 Nuttall and Thierfelder, 3 

 who obtained ripe foetal guinea-pigs, by means of a Csesarean 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. 



3 Ztschr. /. physiol. Chem., Strassburg, 1895, Bd. xxi. S. 109; 1896, Bd. xxii. S. 62. 



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