76 PHYSIOLOGY 



class of amino-acids, and must be regarded as the proximate constituents of 

 the protein molecule. 



A similar hydrolytic change may be effected by the use of digestive 

 ferments obtained either from the alimentary canal of higher vertebrates or 

 from certain plants. Thus we may use pepsin, the active constituent of the 

 gastric juice, trypsin, the proteolytic ferment secreted by the pancreas, 

 papain, or other vegetable ferments obtained from papaya, from pineapple 

 juice, and so on. These ferments are all milder in their action than the 

 strong acids. Pepsin for instance effects only a partial decomposition of the 

 protein molecule. Its action results in the formation of substances which 

 still present all the protein reactions and are classified as hydrated proteins 

 or as proteoses and peptones. Trypsin carries the protein a stage further 

 and gives a mixture of amino-acids. Certain groups however of the protein 

 molecule present a considerable resistance to the action of trypsin, so that 

 when its action is complete these groups are still found not yet broken down 

 into their constituent amino-acids. 



The putrefactive processes determined by the process of bacteria in 

 solutions of proteins are somewhat too complicated in their results to throw 

 much illumination on the structure of the protein molecule itself. This 

 method is however of extreme value when it is applied to isolated con- 

 stituents of the proteins. Under the action of these bacteria we may have a 

 process of deamination which may be accompanied by simple hydrolysis or 

 by reduction. In the former case an amino-acid may be converted into 

 an oxyacid, in the latter case into a fatty acid. 



Thus tyrosine under the action of bacteria of putrefaction may split up 

 into ammonia and oxyphenyl propionic acid. 



OH.C 6 H 4 .CH 2 .CHNH 2 .COOH + H = 

 HO.C 6 H 4 .CH 2 .CH 2 .COOH 



Under the action of yeasts an amine may become an alcohol. 

 C 5 H n .NH 2 + H 2 - C 6 H U .OH + NH 3 



(amylamine) (amylalcohol) 



On the other hand, the effect of the bacteria may be to split off carbon 

 dioxide from the amino-acids. Thus, the diamino-acid, lysine, 



CH 2 NH 2 



I ' I 



CH 2 CH 2 



I I 



CH 2 becomes CH 2 pentamethylene diamine. 



I ' I 



CH 2 CH 2 



I ' II 



CH.NH 2 CHaNH., 



I 

 COOH 



Tyrosine becomes p. oxyphenylethylamine, a substance having marked 



