708 METABOLISM 



presence in the blood of decomposition products of glucose ; (3) that it 

 is due to a special hormone produced from some ductless gland. Con- 

 cerning the first of these possibilities, it is supposed that the mechanism 

 involved is dependent on the law of mass action ; namely, that glycogen be- 

 comes converted into glucose whenever the blood flowing to the liver con- 

 tains less than its normal concentration of glucose, and conversely, when this 

 blood contains an excess of glucose, as during absorption, that a glycogen- 

 building process occurs. Although there can be little doubt that the process 

 of glycogen formation or destruction will depend to a certain extent 

 upon the amount of glucose present in the blood flowing to the liver 

 cells, yet it is impossible that this can be an important means in the 

 control that exists between sugar production by the liver and sugar 

 consumption by the tissues, because the sugar that is added to the portal 

 blood during absorption would mask any depletion caused by sugar 

 consumption. 



The second possibility that the hormone is some decomposition prod- 

 uct of glucose would appear to have some support, if we consider this 

 hormone to be an acid product (carbon dioxide or lactic acid) produced by 

 sugar metabolism, for it is known that an increase in the hydrogen-ion 

 concentration of the blood flowing to the liver cells excites a glycogen- 

 olysis. As we have already seen, however, it is difficult to secure ex- 

 perimental evidence, in anesthetized animals at least, that glycogen- 

 olytic activity is readily excited in this way. 



The third possibility that some specific hormone may exist in the 

 blood exciting the glycogenolytic process is investigated by producing 

 disturbances involving various of the ductless glands, particularly the 

 pancreas, the adrenals, the parathyroids and the pituitary. The influ- 

 ence of certain of these glands may be closely bound up with that 

 exercised through the nervous control, as we have seen to be the case 

 with the adrenal gland. Whether it is by the production of hormones 

 directly necessary for proper carbohydrate metabolism, or by the re- 

 moval from the -blood of such substances as interfere with this process, 

 that the ductless glands functionate, is one of the main problems we 

 have to consider. , 



Utilization of Glucose in Tissues. Although the experimental diabetes 

 induced by disturbances in the function of the ductless glands is dependent 

 in the first instance on an upset of the glycogenic function and later on glu- 

 coneogenesis, the utilization of glucose in the tissues ultimately becomes 

 interfered with. It is therefore important that we should digress for a 

 moment to consider briefly what is known regarding the process by 

 which sugar becomes utilized in the organism. That glucose becomes 

 used up by active muscle there can be no doubt. Thus, if the muscles 



