34 



THE PROTEINS. 



CLASSIFICATION OF THE PRINCIPAL PROTEIN COMPOUNDS. 



Proteins 



Compound 

 proteins 



I Albuminoids - 



Coagulated albumin. 



Mucin. 

 Hemoglobin. 

 Nucleoalbumin. 

 Nuclein. 



f Keratin. 



Elastin. 



Collagen. 



Gelatin. 

 I Etc. 



ALBUMINOUS SUBSTANCES. 



These are sometimes called proteins, though it is 

 more convenient to reserve this name for the whole class, 

 including also the albuminoids. They form the principal 

 part of the protoplasm which is found in animal and plant 

 cells. The constitution of the molecule and even the 

 exact formula of the different members of the group is 

 uncertain. They are known to be very complex, those 

 which have been most studied having several hundred 

 atoms' in a molecule. They differ somewhat from each 

 other in composition, but their constituents usually lie 

 within the following limits; 



