ACTION OF MICRO-ORGANISMS 203 



Other forms of organisms produce different end products ; 

 thus instead of alcoholic fermentation we may have the 

 formation of acetic, butyric or lactic acids, acetone, etc. 

 The different kinds of carbohydrates are acted upon to 

 different degrees by different forms of bacteria, hence the 

 behaviour of an organism towards the various sugars is used 

 as a means of identifying bacteria. 



Most carbohydrates are fairly well dealt with by animals, 

 but one form of carbohydrate is apparently not utilised by 

 higher animals. Cellulose is resistant to the enzymes of the 

 mammalian alimentary canal but it is attacked by micro- 

 organisms. Certain bacteria can dissolve cellulose and use 

 it as a source of energy. By the action of bacteria in the 

 alimentary canal of herbivora cellulose is formed into sub- 

 stances which can be absorbed and used by the animal.* 



The bacterial decomposition of proteins is spoken of as 

 putrefaction. The hydrolysis of proteins into amino acids 

 has been considered under digestion, so we must now consider 

 the action of bacteria upon amino acids. 



The amino acids may be reduced with the formation of 

 ammonia, 



R-CH 2 CH-NH 2 COOH + H 2 -> RCH 2 CH 2 COOH + NH 3 , 

 or they may be oxidised with the formation of ammonia and 

 a ketone acid 



RCH 2 CH-NH 2 -COOH+V 2 2 + RCH 2 COCOOH + NH 3 . 

 A process of oxidation and reduction leading as a net result 

 to an apparent hydrolysis may occur, 



RCH 2 CHNH 2 'COOH+H 2 O ->RC H,CH L CH+NH 8 +CO t . 

 Carbon dioxide maybe removed, leading to the formation of 

 an amine, 



RCH 2 CHNH 2 COOH - --> RCH 2 CH 2 NH 2 + CO 2 . 



The further behaviour of these substances is important. 

 The fatty acids and alcohols are oxidised in the manner 

 described in Chapter X. The amines may affect the blood 

 pressure (see p. 195) and ultimately produce degenerative 

 changes in the blood vessels. The aromatic amino acids give 

 rise to phenolic compounds such as phenol, and to such sub- 

 stances as indole and skatole. The latter are the typical evil- 

 smelling products of putrefaction. By the overgrowth of 

 putrefactive organisms in the intestine such substances are 

 produced and they produce toxic symptoms unless there is 



* H. Pringsheim, Zeit. physiol. Ghent., 1912, vol. 78, p. 266. 



