226 PHYSIOLOGY CHAP. 



contents of the intestine must be very complex, to judge from the 

 copious and dissimilar products that result. There can be no 

 doubt that the intestinal bacteria have a transforming action 

 on carbohydrates, on fats, and on proteins. 



From carbohydrates there arise by fermentation, alcohol, 

 lactic, acetic, benzoic, succinic, butyric, and valerianic acid, with 

 development of carbonic acid gas, methane or marsh gas, and 

 hydrogen (Nencki). What is of greater importance not merely 

 starch, but also cellulose can be digested and decomposed by 

 bacterial activity. Schmulewitsch observed that cellulose can be 

 partly digested by pancreatic juice, because after ligation of 

 Wirsung's duct the quantity of cellulose excreted with the faeces 

 is somewhat increased. But Tappeiner has shown that the greater 

 part of this conversion is effected by the intestinal microbes. On 

 taking weighed parts of the intestinal contents of freshly killed 

 animals, and dividing each into three samples, the first of which 

 is immediately set to digest as it is at body-temperature, the 

 second after sterilisation with an antiseptic, the third after boiling 

 it is seen that the cellulose disappears only in the first sample. 

 If pieces of paper or cotton are placed in the mixture they are 

 dissolved. The importance of this is obvious, particularly for 

 those animals that live exclusively on vegetable matters, since 

 they are enabled not only to utilise a substance that is difficult 

 to digest, but also to render the nutritive substances enclosed in 

 the cuticle of cellulose accessible to the action of the enzymes. 

 In this connection it is interesting to note that if newly hatched 

 chickens are brought up on sterile food, they rapidly decrease in 

 weight, and die, like the controls that are kept fasting (Schottelius, 

 1902). The presence of intestinal microbes is therefore essential 

 to the life of these animals. 



The acid reaction of the contents of the small intestine is due 

 principally to development of the organic acids above enumerated. 



Neutral fats may break up in consequence of intestinal 

 putrefaction into glycerol and fatty acids, 'and the latter may 

 eventually undergo further cleavage, giving rise to the develop- 

 ment of simpler fatty acids. The steapsin of the pancreatic juice 

 is not capable of effecting this, so Landwehr assumed that the 

 capacity of splitting up the higher fatty acids belongs exclusively 

 to the bacteria, since, in his opinion, it ceases altogether in 

 perfectly aseptic, artificial digestions. But this view was shown 

 to be erroneous by Bruno's latest work, referred to above. 



Still more important is the putrefactive action of the intestinal 

 bacteria upon proteins. This is not confined to splitting the large 

 protein molecule into proteoses, peptones, and amido-acids (leucine, 

 tyrosine, aspartic acid), as is the case with pancreatic digestions in 

 an aseptic medium in vitro (Kiihne, Salkowski, Salomon, Hiifner) ; 

 but the decomposition is carried further, to the development of 



