100 PHYSIOLOGY 



(3) and (4) are sometimes spoken of as the enolic form. If we con- 

 sider that perhaps some hundred of the amino-acid groups may go to 

 making up a single protein molecule, it is possible to form some con- 

 ception of the enormous variability in reaction possible to such a 

 compound. 



THE CONSTITUTION OF DIFFERENT PROTEINS 



All the proximate constituents of proteins, so far as we know, 

 are amino-acids. Of these the following have been isolated, namely, 

 glycine, alanine, amino-valerianic acid, leucine, isoleucine, proline, 

 oxyproline, serine, phenyl alanine, glutamic acid, aspartic acid, 

 tyrosine, tryptophane, cystine, lysine, histidine, arginine, and ' di- 

 amino-trioxydodecoic ' acid. 



The question now arises whether all the different varieties of pro- 

 tein owe their peculiarities to the presence of different amino-acids or 

 whether the greater number of the amino-acids above mentioned are 

 present in all proteins, the differences between the latter being deter- 

 mined by differences in the arrangement and relative amounts of their 

 proximate constituents. A large number of analyses of different 

 proteins have been made by Abderhalden, Osborne, and others, 

 utilising the methods for the isolation of amino-acids devised by 

 Fischer. The constitution of some representative proteins as 

 determined in this way are given in the following Table : 



JheStf results ^sjaow that all the proteins contain a very considerable 



