PHYSIOLOGICAL CHEMISTRY 405 



necessary for bacterial growth are very favourable in the intestine. 

 As a result of their growth, bacteria 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. In the small 

 intestine the bacteria which are most active are those acting on carbo- 

 hydrates, whereas in the large intestine these are largely replaced by 

 bacteria acting on protein. 



Their action on proteins leads to the production of proteoses, peptones, 

 and amino acids, etc. So far their action corresponds to that of trypsin, 

 but they digest farther and produce a multitude of simple degradation 

 products, such as ammonia, fat acids, carbonic acid, etc., as well as a 

 group of substances belonging to the aromatic series. 



The aromatic bodies are arranged in two groups. The one contains 



PTT 



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

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



O1T 



formula C 6 H 4 <V,jj CH(NH ) COOH ^ nen tn * s cnan g es i nto kresol 

 and phenol, the amino-propionic acid side -chain loses, first its amino 

 group as ammonia, and then its carboxyl and methyl group are 

 oxidised and given off as carbonic acid and water. 



The other group is more complex, and contains indol C 6 

 and its methyl derivative skatol 



/CH 3 



These are derived from tryptophane, a product of the tryptic digestion 

 of certain proteins. Its chemical reactions and constitution are described 

 on p. 395. 



Anaerobic bacteria first of all act on the tyrosin and tryptophane, 

 and split off from them the amino (NH 2 ) groups as NH 3 . After this 

 has been accomplished, aerobic organisms act on the remaining side 

 chains yielding carbon dioxide and water. 



Certain of these aromatic bodies especially skatol have a strong 

 faeculent odour which they impart to the faeces. Considerable pro- 

 portions of them are, however, absorbed into the blood and reappear 

 in the urine as indoxyl and skatoxyl in combination with sulphuric 

 acid and alkalies as aromatic sulphates (see p. 435). 



These above products also result when proteins undergo putrefaction 

 in vitro, but in this latter case other bodies called ptomaines are also 

 produced. These are powerful poisons and it is on account of their 

 presence that it is dangerous to eat putrid flesh. 



