Chemical Constituents of the Animal Body. 259 



These are for the most part quite simple products, which 

 yield on hydrolysis only two amino-acids. As examples, 

 glycyl tyrosine and alanyl glycine, which have been 

 obtained from silk, may be mentioned. 



By treatment with weak solutions of acids (0*4 per 

 cent, sulphuric acid) or alkalis (O'l per cent, sodium 

 hydroxide) at 40, proteins undergo a slight change and 

 yield the so-called acid or alkali albumins. These are 

 insoluble in water, but soluble in excess of alkalis and 

 acids. A scission of only a small number of amino-acid 

 groups takes place in the formation of these products, 

 which are sometimes known as the metaproteins. By 

 hydrolysis of certain proteins with 12 per cent, hydro- 

 chloric acid at 40, a series of apparently pure products 

 known as " kyrines " have been obtained, which were 

 purified by precipitation as phosphotungstates. 



The most interesting intermediary hydrolysis products 

 of the proteins are, however, those obtained by the action 

 of ferments. The gastric juice contains such a substance 

 which readily degrades most (but not by any means all) 

 proteins at 37 in the presence of acids (N/20 hydrochloric 

 acid). The pancreas also secretes a liquid containing a 

 ferment,* which digests proteins in alkaline solutions (0*5 

 per cent, sodium carbonate). If the general formula of the 

 protein is referred to 



B' K" R" 



I \ \ 



NH 2 CH CO-i-NH CH CO- 



-NH CH 



CO 



R" 

 --NH CH 



COOH 



* Or rather, a ferment-yielding substance (preferment) from which a fer- 

 ment is generated when the secretion comes in contact with the mucous mem- 

 brane of the small intestine, which contains the so-called entero kinase. 



