208 BLOOD SUGAR 



dialysis against blood, sugar will not enter the blood or 

 diffuse from it; and in the author's opinion have, by this 

 "method of osmotic compensation," furnished the final 

 proof that the sugar exists free in the blood or at least in a 

 condition to become free spontaneously. 



"Sucre Immediat" and "Sucre Virtuel." A second 

 question, however, presents itself : whether we may assume 

 that the total amount of sugar in the blood is in free form. 

 From this point of view the writer regards the results of Le- 

 pine and Boulud, 50 after a long series of careful studies, as 

 apropos. These authors differentiate in the blood between 

 " sucre immediat" and "sucre virtuel." The first is de- 

 termined by catching the blood directly in an acid solution 

 of mercuric nitrate, filtering, pressing the blood cake dry and 

 determining the sugar in the collected filtrate after separa- 

 tion of the mercury. The virtual sugar, supposed to be 

 combined in the blood as glucosides, is determined from the 

 increase of reduction power observed in the blood after 

 keeping it for an hour in the incubator with added invertin 

 or emulsin before estimating the sugar. Apparently, 

 however, the conversion of the virtual sugar into the de- 

 terminable form will take place spontaneously if it be al- 

 lowed to stand for a quarter of an hour; and it has been 

 proposed to always allow fifteen minutes to elapse after 

 withdrawal of the blood before beginning the sugar estima- 

 tion. 51 It is obvious from this that in the above noted 

 diffusion experiments the virtual sugar must in reality 

 appear as free sugar. 



Does the Blood Contain Other Carbohydrates in Addition 

 to Glucose? It may, therefore, be asked what significance 

 is to be ascribed to the "sucre virtu el "f This is certainly 

 not a simple matter. The French authors, for example, con- 

 tinue to speak of "sucre virtuel" even after heating the 



80 R. Lupine and Boulud, Jour, de Physiol., 11, 12, 557, 1909; 13, 178, 1911; 

 and a number of other contributions in C. R. and C. R. Soc. de Biol. 



M E. Frank (Wiesbaden), Zeitschr. f. physiol. Chem., 70, 129, 1910. 



