5 2 6 TEXT-BOOK OF PHYSIOLOGY 



where it exerts its influence. Since the discovery of the islets of Langerhans 

 in the body of the pancreas it has come to be believed that the cells composing 

 these islets, rather than the cells lining the pancreatic acini generate the 

 specific material. This view is supported by the fact that in many cases of 

 persistent and fatal glycosuria in man, there is in the large majority of cases, 

 a concomitant lesion of these islets. The route by which the secreted mate- 

 rial reaches the blood is thought to be through the lymph- vessels and thoracic 

 duct, for ligation of this latter vessel is followed by glycosuria. 



As to the manner in which the specific material prevents and its removal 

 gives rise to glycosuria, two theories at least are supported by facts and are 

 more or less plausible, viz. : 



1. That it promotes the oxidation (glycolysis) of sugar. 



2. That it prevents a too rapid production of sugar on the part of the liver cells. 



It is assumed according to the first view that there is present in the mus- 

 cles, an enzyme, the action of which is the disruption of the sugar molecule 

 and thereby promotes its oxidation; but that for the manifestation of its 

 power it requires the activating influence of the pancreatic hormone, for in 

 its absence oxidation of sugar does not take place and hence with the con- 

 tinual production of sugar by the liver cells, hyperglycemia and glycosuria 

 result. This view has received confirmation in recent years from the results 

 of the experimental work of Knowlton and Starling. These investigators 

 were able, by employing a heart-lung preparation of a normal dog, to keep 

 the heart beating for several hours in a practically normal manner by causing 

 blood of the same animal to circulate through its cavities and the coronary 

 system at the rate of about 300 c.c. every two minutes. To this blood glucose 

 was added. At the end of the experiment it was found that the amount of 

 sugar oxidized was, on the average, 4 milligrams per gram of heart-muscle 

 per hour. On substituting the heart-lung preparation of a dog that had 

 been rendered diabetic by the removal of the pancreas it was found that the 

 power of consuming sugar was reduced to a minimum or altogether lost by 

 reason presumably of the absence of the pancreatic hormone. They then 

 demonstrated that the heart of the diabetic animal acquired a sugar-consum- 

 ing or oxidizing power on feeding it with the blood of a normal animal, the 

 consumption being in one animal 2.9, 5.8, 8.1 milligrams per gram of heart- 

 muscle in three consecutive hours, and in another experiment there was an 

 average consumption of 3.55 milligrams. In another series of experiments 

 it was demonstrated that the diabetic heart very promptly developed a sugar- 

 consuming power on the addition to the blood of a boiled extract of the pan- 

 creas the consumption rising from almost nothing to 4 milligrams in the 

 second hour. The deduction from these experiments is that the oxidation 

 of sugar in the muscle, is dependent on the presence of a specific hormone 

 secreted by the pancreas. If this same fact could be established for skeletal 

 muscle, the view that the pancreatic hormone promotes and its absence pre- 

 vents the oxidation of sugar would be generally acceptable. 



It is assumed by the supporters of the second view that the production 

 of sugar in the liver cells is regulated by two opposing factors or hormones, 

 that secreted by the adrenal glands and that secreted by the pancreas, the 

 former exciting, the latter inhibiting the process. In the absence of the 

 pancreatic hormone the adrenal hormone unduly excites the production of 

 sugar. The following facts support this view: After extirpation of the adre- 



