238 PEACT1CAL PHYSIOLOGY. 



converts it into trypsin. On a flesh-free diet, the pancreatic juice, as 

 secreted from the duct of Wirsung, contains very little trypsin, and 

 digests coagulated egg white scarcely perceptibly even after several 

 hours. If to this inactive pancreatic juice a few drops of succus 

 entericus be added digestion of the egg white proceeds actively. 

 Trypsinogen, which is the form in which the proteolytic ferment is 

 secreted on a flesh-free diet, remains inactive until it gets to the 

 intestine where it is converted into trypsin by the entero-kinase. 

 Entero-kinase is not secreted unless it is required, i.e. if the intestinal 

 mucosa be mechanically stimulated a juice will be secreted containing, 

 however, no entero-kinase. 



Bacterial Digestion. As has been explained above, the conditions 

 necessary for bacterial growth are very favourable in the upper reaches 

 of the intestine. As a result of their growth they decompose the food- 

 stuffs and lead to the production of products in many cases the same as 

 those of the digestive juices, in other cases of a different nature. 



Their action on proteids leads to the production of proteoses, 

 peptones, and amido acids. So far their action corresponds to that of 

 pepsin, but they produce other substances belonging to the aromatic 

 bodies. 



These are arranged in two groups of bodies. The one contains 



PTT 



phenol C 6 H 5 OH and its methyl derivative kresol C 6 H 4 <Qjj 3 . These 



are produced from tyrosin, which, it will be remembered, has the 



OTT 

 formula C 6 H 4 <Qjj OHYNKH COOH an( ^ w ^ en ^ changes into these 



bodies, the amido propionic acid side chain loses first its amido group 

 as ammonia, and then its carboxyl and methyl groups are oxidised 

 and given off as carbonic acid and water. 



The other group is more complex, and contains indol C 6 H 4 <Q j^ 

 and its methyl derivative skatol 



These are derived from tryptophan, a product of tryptic digestion of 

 true proteids. Its chemical reactions are described on p. 452. Its 

 chemical constitution is skatol amido acetic acid 



/CH 3 



C 6 H 4<NH> - CH(NH 2 )COOH. 



It is anaerobic bacteria which first of all act on the tyrosin and 

 tryptophan, and split off from them the amido (NH 2 ) groups as NH 3 . 



