1172 PROTEIDS. 



Class III. Globulins. 



Besides the derived albumins there are a number of native 

 proteids which differ from the albumins in not being soluble in 

 distilled water; they need for their solution the presence of an 

 appreciable, though it may be a small, quantity of a neutral 

 saline substance such as sodium chloride. Thus they resemble 

 the albuminates in not being soluble in distilled water, but 

 differ from them in being soluble in dilute sodium chloride or 

 other neutral saline solutions. Their general characters may 

 be stated as follows. 



They are insoluble in water, soluble in dilute (1 p.c.) solu- 

 tions of sodium chloride; thev are also soluble in dilute acids 

 and alkalis, being changed on solution into acid- and alkali- 

 albumin respectively unless the acids and alkalis are exceedingly 

 dilute and their action is not prolonged. The saturation with 

 solid sodium chloride or other neutral salts of their saline solu- 

 tions, precipitates most members of this class. 



1. Crystallin. (Globulin of the crystalline lens.') 



This form of globulin is usually regarded as identical with 

 vitellin. It is however convenient to treat it separately inas- 

 much as it can be prepared in a pure form, whereas vitellin has 

 not as yet been obtained free from lecithin. 



Crystalline lenses are rubbed up in a mortar with a little 

 fine sand and a few crystals of rock salt; the mass is then 

 extracted with water and filtered. The filtrate contains the 

 crystallin and some serum-albumin. The former is separated 

 from the latter by copious dilution with distilled water and 

 passing a current of carbon dioxide through the diluted mix- 

 ture, whereupon the crystallin is precipitated. 



According to the latest researches the lens contains two 

 globulins which differ slightly in their precipitability and in 

 the temperatures at which their solutions coagulate. 



2. Vitellin. 



This constitutes the characteristic proteid constituent of 

 egg-yolk. Some at least of the globulins present in vegetable 

 protoplasm and more particularly in the crystals of the aleurone 

 grains, appear to be identical in their general properties and 

 reactions with vitellin. As obtained in conjunction with some 

 lecithin by exhaustion of egg-yolk with ether, it consists of a 

 white, pasty, granular mass, insoluble in water, readily soluble 

 in solutions of sodium chloride which may be easily filtered. 

 Unlike other true globulins it cannot be precipitated from this 

 solution by saturation with sodium chloride. Its saline solu- 



