QUANTITY AND COMPOSITION OF BLOOD 977 



THE GLOBULINS. The globulins of serum, known as para- 

 globulin or serum globulin, are obtained by half -saturation with 

 ammonium sulphate. Their solutions in salt coagulate at about |75 C. 

 Since globulin is insoluble in distilled water it is precipitated on 

 dialysing serum against distilled water. The precipitate obtained in 

 this way is not, however, so great in extent as that obtained on half- 

 saturation, and on this account the globulin fraction of the serum 

 proteins has been divided into two fractions, namely, euglobulin, 

 precipitable by dialysis, and pseudo- globulin, not precipitable by 

 dialysis, but thrown down on half-saturation with ammonium sulphate. 



A thorough study of serum globulin by Hardy has shown that 

 this body forms adsorption combinations with acids, alkalies, or 

 neutral salts. With acids and alkalies the globulin forms ' salts ' which 

 ionise in solution so that in an electric field the entire mass of protein 

 moves. These salts cannot be precipitated by dialysis. In them the 

 globulin acts much more strongly as an acid than as a base, so that a 

 weak acid, such as acetic acid, has a much smaller dissolving power 

 over globulin than has the equivalent amount of hydrochloric acid, 

 and boracic acid has a very slight power indeed. The weak basic 

 character of globulin causes its salts in weak acids to undergo hydro- 

 lysis with separation of globulin, so that in order to reach the same 

 grade of solution with a weak acid as with a strong acid a great excess of 

 the acid is necessary. Owing to the much stronger acid character of 

 globulin it is found that weak ammonia dissolves it almost as well as 

 strong alkalies. With neutral salts globulins form molecular compounds 

 which are soluble, but are readily decomposed by water with liberation 

 of the insoluble globulin. They are therefore only stable in the presence 

 of a comparatively large excess of salt. The globulins differ from the 

 albumens of the serum in containing constantly organic phosphorus 

 as an integral part of their molecule. In all its solutions globulin is 

 present in large molecular aggregates, so that it is impossible to filter 

 a globulin solution through a porous clay cell. 



THE CONDITION OF THE PROTEINS IN THE BLOOD-SERUM. 



Although it is easy by such simple means as the addition or removal 

 of neutral salts to separate one or more different forms of protein 

 from serum, we have strong evidence that these proteins do not exist 

 side by side in the serum, but are combined to form what we may 

 term serum protein, which acts as a whole and differs in its qualities 

 from many of those of its constituent globulins or albumens. When 

 a current is passed through blood- serum no movement of protein 

 takes place (Hardy). Alkali globulin therefore cannot be present. Salt 

 globulin might be assumed to be present since it does not ionise in 

 solution, but serum is not precipitated by simple addition of acid, 



62 



