PROTEINS OR ALBUMINOUS SUBSTANCES 425 



former are subjected to heat, and are destructively distilled they 

 yield a foetid liquid which smells ammoniacal and acts like an 

 alkali on test paper. Wood and vegetable matter, on the other 

 hand, give an acid distillate. But such insight as the chemical 

 physiologist now enjoys into the constitution of the proteins is 

 the result of researches which have been accomplished almost 

 entirely within the last twenty years. 



The large number of apparently distinct compounds which, 

 presenting as they do few of the characters by which pure 

 chemical individuals are usually recognised, renders the investiga- 

 tion of the proteins one of the most difficult tasks undertaken 

 by the chemist. An attempt has been made to classify these 

 substances, and provisionally we may accept the scheme which 

 has been brought forward, with the assurance that, while 

 temporarily useful, the results of further work will lead perhaps 

 to new classes, certainly to some modification in those already 

 recognised. The scheme set forth below results from the work 

 of a Committee of the American Society of Biological Chemists 

 (1908). It includes vegetable as well as animal proteins. 



I. The Simple Proteins. 



a. Albumins. 

 6. Globulins. 



c. Glutelins. 



d. Prolamins. 



e. Scleroproteins or albuminoids. 

 /, His tones. 



g. Protamines. 



II. Conjugated Proteins. 



a. Nucleoproteins. 



b. Glycoproteins. 



c. Phosphoproteins. 



d. Haemoglobins. 



e. Lecithoproteins. 



JIT, Derived Proteins. 



1 . Primary Protein Derivatives. 

 a. Proteans. 

 6. Metaproteins. 

 c. Coagulated Proteins. 



