82 A. I. RINGER 



is achieved a satisfactory' chemical classification will not be possible. All 

 the known proteins possess certain chemical and physical properties in 

 common, and differ in others. The classification at present is based on 

 these differences. It is based upon differences in their solubilities, coagu- 

 lations, precipitations, etc. It is a crude, and more strictly physical than 

 chemical classification, but it answers the purpose to a certain extent by 

 bringing some order out of chaos. 



The proteins are divided into three main groups : 



I. The simple proteins which yield on hydrolysis a-amino acids. 



II.- Conjugated proteins which are composed of simple proteins chem- 

 ically united with another organic compound. 



III. Derived proteins which are proteins that are found in the in- 

 complete digestion or hydrolysis of either of the above naturally occurring 

 protein. 



These three main groups may be further subdivided into the follow- 

 ing groups : 



I. Simple Proteins. 



a. Albumins 



b. Globulins 



c. Glutelins 



d. Prolamiris (alcohol soluble proteins) 



e. Albuminoids or Sclero proteins 



f. Histones 



g. Protamins 



II. Conjugated Proteins. 



a. Nucleoproteins 



b. Glucoproteins 



c. Phosphoproteins 



d. Chromoproteins 



e. Lentoproteins 



III. Derived Proteins. 



A. Primary B. Secondary 



a. Proteins a. Proteoses 



b. Metaproteins b. Peptones 



c. Coagulated proteins c. Peptides 



The albumins are present extensively in the animal and plant king- 

 doms. The most important ones of this group are serumalbumin (from 

 blood), ovalbumin (from the white of egg), lactalbumin (from milk). 



As a class they are characterized by their solubility in distilled water, 

 dilute acid and alkali. In the presence of neutral salts they are coagulated 



