10 GERM-CELL CYCLE IN ANIMALS 



ciates into electro-positive Na ions (cations) and 

 electro-negative Cl ions (anions). Colloidal par- 

 ticles are likewise electrically charged, those of acid 

 colloids usually negatively and those of alkaline 

 colloids positively. The union and separation of 

 particles and their consequent rearrangement cause 

 gelation, liquefaction, etc. ; it is thus evident that 

 many physiological activities may be due to the 

 electrical charges of ions instead of the chemical 

 nature of the particles themselves. Cellular struc- 

 tures therefore depend upon the tendency of col- 

 loidal particles to form aggregates (gelation, coagula- 

 tion), and more or less upon the electrically charged 

 nature of the particles. 



The most characteristic chemical constituents of 

 protoplasm are the proteins. The most common 

 proteins in the body show on the average the follow- 

 ing percentage of elements : 



Carbon 50 -55 % 



Hydrogen 6.5- 7.3% 



Nitrogen 15 -17.6% 



Oxygen 19 -24 % 



Sulphur 3- 2.4% 



Proteins may be separated into three groups : (1) 

 simple proteins, such as protamines, albumins, and 

 globulins; (2) conjugated proteins, the glucopro- 

 teins, nucleoproteins, and chromoproteins ; and 

 (3) the products of protein hydrolysis, infraproteins, 

 proteoses, peptones, and polypeptides. These have 

 been studied both by microchemical and macro- 

 chemical methods. In the former method reagents 

 are applied to the microscopic objects and the 



