THE liLOOl) SrCAU (;.')! 



B}' the latter term is meant sugar in the blooti wliich does not lj(;liavo 

 physically like glucose in aqueous solution nor respond to the ordinary 

 chemical tests for sugar, but from which free glucoses may be reliberated 

 by such simple procetlures as boiling witli dilute a(;ids. Such sugar 

 is supposed to exist as a eomponcMit of particles having tlu; larger di- 

 mensions which characterize colloids (non-difTusoids). But as to 

 the actual chemical nature of these a great variety of proposals have 

 been made. Thus Pavy proposed glucose molecules held entire to 

 the colloids of the blood in a state of simple adsori)tion (com[)arable 

 to the state of molecules of a dye electrically bound to particles of a 

 colloid clearing agent). He also proposed glucose chemically incor- 

 porated in the structure of the protein molecule, and between these 

 extremes by the same author a score of suppositions have l)een made by 

 others, among which Drechsel's jecorin, a lecithin-sugar comi)ound, 

 is a notable example. Another worthy of serious consideration is 

 that of glucose built up into polymers intermediate between disac- 

 charides and glycogen. The ba?is for assuming the existence of com- 

 bined sugar in the blood lies chiefly in the observation that following 

 glucose administrations the increase in the reducing power of the blood 

 which results from heating the blood with dilute acid is greater than 

 the increase resulting from the same process before sugar admin- 

 istration (see Pavy, Lepine, Loewi). Also, if glucose is added to fresh 

 blood and the mixture placed in the incubator, the reducing power 

 falls but may be in part rehabihtated by boihng with dilute acid.^" 

 As to the sugar which is determined by the ordinary methods of 

 blood analysis, it would appear that we are dealing almost exclusively 

 with free glucose. As yet no one has succeeded in proving the exist- 

 ence in blood of a combined sugar capable of spontaneous conversion 

 into free sugar. Michaelis and Rona dialyzed separate portions of the 

 same blood against isotonic salt solutions containing graduated quan- 

 tities of sugar. A sugar solution which neither lost nor gained sugar 

 during the dialysis they regarded as having an amount of free sugar 

 equal to that in the blood. Titration of the blood sugar and of the 

 sugar in such a solution gave almost identical figures. They accord- 

 ingly concluded that all of the reducing sugar in this blood muse have 

 been as free to diffuse as was that in the simple salt solution. But this 

 ingenious experiment of Michaelis and Rona does not show conclusively 

 that in circulating blood there is no sugar in a state of colloidal 

 adsorption, because drawn blood rapidly undergoes survival changes 

 (e. g., lactic acid formation) which might influence the affinity of its 

 colloids for sugar. However, McGuigan and Hess" led the blood of 

 living animals through collodion tubes enclosed in jackets filled with 

 isotonic salt solutions and found that when equiUbrium was established 



1" A critical review of the literature to 1912 will be found in the books by 

 McLeod and Allen. Compare also the article by Levene and the recent studies 

 of Lombroso favoring the polvnierization idea. 



" Jour. Pharm. and Exp. Ther.. (1914) (ti), 45. 



