CLASSIFICATION 425 



all proteins, are precipitated by complete saturation with 

 ammonium sulphate. 



Traces of albumins occur in practically all seeds, but 

 no seeds, so far examined, have been found to contain 

 large quantities. 



While plant albumins resemble those of animal origin 

 in regard to the two essential features of this group, 

 namely, solubility in water and coagulation by heat, they 

 differ in regard to their behaviour towards strong solutions 

 of inorganic salts. Thus animal albumins are not sup- 

 posed to be precipitated by half saturation with ammoniun 

 sulphate or saturation with sodium chloride or magnesium 

 sulphate, but this is not always found to be the case for 

 vegetable proteins, many of which are precipitated under 

 these conditions. 

 Globulins. — These are exemplified by serum globulin, fibrinogen 

 and myosinogen, and also the derivatives of the two latter, 

 fibrin and myosin. Examples of vegetable globulins are 

 furnished by conglutin from the seeds of Lupinus, edestin 

 from the seeds of Cannabis saliva, excelsin from the seeds 

 of Bertholletia excelsa, legumin from the seeds of Pisiini 

 sativum, Vicia Faba, and other Leguminosae, juglansin 

 from the seeds of Jiiglans spp., vicilin from the seeds of 

 Pisum sativum, Vicia Faba, etc., and vignin from the 

 seeds of Vigna sinensis. In brief, globulins are amongst 

 the commonest protein reserves of the higher plants. 



The typical globulins are insoluble in pure water and 

 are coagulated by heat. They are soluble in dilute salt 

 solutions, but are insoluble in stronger salt solutions ; thus, 

 unlike the albumins, they are precipitated by saturation 

 with magnesium sulphate or by only half saturation with 

 ammonium sulphate.* 



* These differences in solubilities between albumins and globulins may 

 be illustrated by dissolving some of the white of an egg in water and placing 

 it in a dialyser ; as the small quantity of sodium chloride contained in the 

 egg-white diffuses out, the globulin is precipitated out of solution ; or, 

 again, if the solution is mixed with an equal volume of saturated ammonium 

 sulphate solution, the globulin will likewise be precipitated out, owing to 

 the solution now being half saturated with ammonium sulphate, but the 

 albumin will remain in solution. 



