70 THE CHEMISTRY OF CATTLE FEEDING 



were formerly called acid and alkali albumins respectively, but 

 are now known as meta-proteins. By continued hydrolytic 

 treatment, e.g. boiling with dilute acid or alkalis, the meta- 

 proteins undergo further change and the products are described 

 as proteoses and peptones. Similar changes are produced by 

 ferments of various kinds, both organised and formless, e.g. 

 bacteria, pepsin, etc. 



Metaproteins, proteoses, and peptones are not distinct, well- 

 defined classes of compounds, but merely transition products. 

 They are to be regarded as recognisable stages in the gradual 

 process of dissociation of the proteins. They readily undergo 

 further hydrolysis and are transformed into polypeptides (p. 61) 

 and finally into amino-acids. Provided the acid is not too 

 strong and the action is not unduly prolonged, the amino-acids 

 are obtained with the carbon chains apparently intact and the 

 nitrogen atoms in their original positions. They are called 

 primary dissociation products to distinguish them from the 

 products of further change in which the amino-acids are split 

 up or altered. The latter are called secondary dissociation 

 products. 



Glycocine, alanine, serine, lencine, asparagine, arginine, 

 histidine, cystine, tyrosine, and tryptophane (p. 52) are 

 amongst the most important of the primary dissociation 

 products, but there are many others. The kinds and quantities 

 of the primary dissociation products are characteristic of the 

 type of protein from which they are obtained. 



It is to be supposed, therefore : (i) that the proteins are 

 complex aggregates of the radicles of these compounds ; (2) 

 that the nature of the union is similar to that of the polypep- 

 tides. In short, it appears that the proteins are merely 

 complex polypeptides, and that the properties of the individual 

 compounds depend upon (a) the particular amino-acids which 

 enter into their composition, and (b) the relative proportions in 

 which they are present. 



The process by which one kind of protein is converted into 

 another as, for instance, in the formation of animal tissues 

 from vegetable foods appears to consist in the resolution of 

 the protein into primary dissociation products which are then 



