866 PHYSIOLOGY 



or in the crystalline form by slight acidification, as in Hopkin's method 

 described on p. 80. Serum albumen is soluble in distilled water. Its 

 solutions therefore can be dialysed indefinitely without any precipitation 

 taking place. 



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 salt in weak acids 

 to undergo hydrolysis 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 preci- 

 pitated by simple addition of acid, which would readily precipitate salt 



