THE METABOLISM OF THE CARBOHYDRATES 677 



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 at 

 first dependent on an upset of the glycogenic function and later of 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 knoAvn 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 

 of one leg in the frog are tetanized, the glycogen content, compared with 

 that of the other leg, will be found to be diminished. 



At first sight it migh.t appear that the easiest way to study the utiliza- 

 tion of glucose in the muscles Avould be to compare its concentrations 

 in the blood flowing to and coming from the muscle. The muscle that 

 has been most successfully employed in studies of this kind has been the 

 heart. Some years ago Starling and Knowlton 24 examined the consump- 

 tion of sugar by the excised mammalian heart, and in their earlier 

 experiments seemed to be able to show that the extent to which this 

 consumption occurred was 4 milligrams per 100 grams heart muscle 

 per hour. A more thorough repetition of these experiments later by Pat- 

 terson and Starling 25 showed, however, that the results can furnish no 

 criterion of the actual consumption of glucose by the tissue on account 

 of the fact that the tissue itself may store away large quantities of 

 carbohydrate in an unused state i. e., as glycogen. 



Other investigators have thought to study the utilization of glucose 

 by observing the rate at which it disappears from drawn blood kept in 

 a sterile condition at body temperature for some hours after death. 

 This process is called glycolysis, and it has been assumed that the process 

 is similar to that which occurs in the tissues themselves an assumption, 

 however, for Avhich there is no warranty. Indeed, it may readily be 

 shown that the glycolysis occurring in blood has very little if anything 

 to do with the utilization of sugar in the tissues, for it has been found 

 that glucose disappears from drawn blood very slowly indeed when 



