230 PHYSIOLOGICAL CHEMISTRY. 



Magnesium sulphate, added in powder form to saturation, is sometimes 

 used in the place of ammonium sulphate to effect the separation of the 

 albumin and globulin. The reaction in both cases depends on the fact that 

 serum albumin may be salted out only with great difficulty. 



It is an interesting fact that other proteins do not appear 

 to be present in the blood. The various proteins consumed 

 as food suffer peculiar changes somewhere in the body and are 

 converted into these two. These in turn serve for the prep- 

 aration of the various other related bodies found in the several 

 tissues of the organism. Gelatin may be formed in this way 

 from the proteins of the blood, but it does not appear that 

 gelatin can replace other proteins as a food since it is deficient 

 in one of the essential protein component groups, viz. : the 

 tyrosine group. 



It is not yet known how constant the relation of serum albu- 

 min to serum globulin is or whether this relation is the same 

 in all kinds of blood. Egg albumin is not equivalent to serum 

 albumin physiologically, since if injected into the blood it 

 appears soon unchanged in the urine. The albumins of re- 

 lated animal species seem to be nearly alike, but this does not 

 hold absolutely true for animals of widely different species. 



THE SUGAR OF THE BLOOD. 



This is found in the plasma and has generally been assumed 

 to be glucose, C 6 H 12 O G , although good reasons may be as- 

 signed for the assumption of other sugars as well. Ordi- 

 narily the simple sugar finally formed in the digestive process 

 is glucose and the possible passage of other sugars into the 

 blood has commonly been overlooked. As the amount of 

 sugar in the blood is small, about o. 1 5 per cent in the mean, its 

 certain identification is a matter of extreme difficulty; it must 

 be remembered that separation from the large amounts of pro- 

 teins present must be complete before any accurate identifica- 

 tion of the remaining trace of sugar may be thought of. The 

 older observers depended almost solely on the common reduc- 

 tion tests which are not very sensitive in dealing with traces. 

 Recent investigators have shown that a left-rotating sugar is 



