84 PHYSIOLOGY 



condenser either with concentrated hydrochloric acid or with a 25 

 per cent, sulphuric acid. Hydrochloric acid was first made use of 

 by Hlasiwetz and Habermann, who added a certain amount of 

 stannous chloride to the mixture in order to prevent any oxidation 

 taking place. We obtain in this way an acid fluid containing an 

 extremely complex mixture of various substances, all of which belong 

 to the 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 verte- 

 brates or from certain plants. Thus we may use pepsin, the active 

 constituent of the gastric juice, trypsin, the proteolytic ferment 

 secreted by the pancreas, papaine 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, 

 only effects 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 presence 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 constituents 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 ammo-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 2 = 

 HO.C 6 H 4 .CH 2 .CH 2 .COOH + NH ;J 



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 



