546 METABOLISM, NUTRITION AND DIETETICS 



The following scheme, doubtless incomplete, illustrates a probable 

 chemical sequence through which the interconversion of alanin, lactic 

 acid, methylglyoxal and dextrose may be brought about by reactions 

 only involving the addition or removal of water or ammonia (Dakin) : 



Dextrose 



Lactic acid Zl Methylglyoxal Z Alanin 

 (CH 3 .CHOH.COOH) (CH 3 .CO.CHO) (CH 3 .CH.NH 2 .COOH) 



Since pyruvic acid can be reduced to lactic acid, any reaction in 

 which it plays a part in the intermediary metabolism of carbohydrates 

 or proteins can also be fitted into the scheme. 



The more completely the various steps in the metabolism of the 

 three great groups of food substances are unveiled, the more 

 clearly does it appear that, far from being independent circuits, 

 the three currents are constantly exchanging materials with each 

 other. 



It is to be supposed that in many of these transformations 

 enzymes are concerned, although comparatively little is definitely 

 known as to this. Normal blood itself has been credited with a 

 ferment which has the power of destroying sugar (glycolysis). 

 But with rigid aseptic precautions the loss of sugar, even in several 

 hours, is small, and it is doubtful whether such a ferment exists. 

 Even under the most favourable circumstances the quantity of 

 dextrose which blood can destroy is so small a fraction of that which 

 disappears in the same time in the body, that it is probably of no 

 importance in carbo-hydrate metabolism (Macleod). On the 

 other hand, Cohnheim stated that while no glycolytic ferment can 

 be demonstrated in the pancreas, and only an exceedingly weak 

 glycolytic action in muscular tissue (Brunton), by combining ex- 

 tracts of pancreas and extracts of muscles, distinct glycolysis, due 

 to a ferment action, could be produced. He suggested that the 

 glycolytic ferment is activated by another substance, as trypsinogen 

 is activated by enterokinase (p. 372). This announcement aroused 

 great interest, since it is known that the pancreas is intimately 

 concerned in the metabolism of sugar. That sugar disappears 

 under the conditions of Cohnheim's experiments has been confirmed 

 by a number of observers. But his interpretation of his results has 

 not been generally accepted. According to Levene and Meyer, 

 the dextrose, far from being burnt, seems to be condensed to a poly- 

 saccharide, and can be recovered by hydrolysing this compound 

 when the mixture is acted on by dilute acid. The action of the 

 pancreas- muscle mixture is, therefore, not a true glycolysis. In- 

 deed, of all the tissues investigated by Levene, leucocytes alone can 

 be credited with a real glycolytic action. Excision of the pancreas 

 in dogs causes permanent glycosuria (pancreatic diabetes) (v. Mering 

 and Minkowski), which is prevented if a portion of the pancreas be 



