8 



VETERINARY PHYSIOLOGY 



1. Products of Decomposition 



The native proteins in solution tend to break down into a 

 series of simpler bodies, and this decomposition is greatly hastened 

 by the action of acids or alkalies or of certain enzymes. A series 

 of more and more simple molecules are thus produced which, as 

 they decrease in complexity, give solutions which are less and 

 less colloidal and less and less easily precipitated by alcohol 

 or by neutral salts, till, finally, products are yielded which no 

 longer give the protein tests, which are freely soluble in alcohol, 

 and which have the characteristics of amino acids. Along with 

 these, certain by-products are also given off. 



The different stages of the disintegration of the native protein 

 molecule may be arranged as follows l : 



Native Proteins. 

 Proteoses. 



Peptones. 



Polypeptides. 



Dipeptides. 



Amino Acids 

 (mono- and di-). 



? 



o 



\ 



sag 



o \ 



1 1 



CC QJ 



o = 



H CB 

 '? = 



> 



"o'-^ 



-= ? 



Of the mon-amino acids thus formed, Leucin amino-caproic 

 acid is generally the most abundant. 



Of the mon-amino acids linked to the benzene nucleus, Tyrosin 

 in which amino-proprionic acid is linked to a benzene ring 

 with one H replaced by OH is the most important. 



1 For a short account of the chemistry of these products of disintegration 

 see Appendix. 



