678 METABOLISM 



compared with the rate at which it disappears from the blood of animals 

 in which the addition of glucose from the liver has been prevented by 

 removal of this viscus (Macleod). 26 



A third method for studying the utilization of glucose consists in 

 observing the respiratory exchange of animals. In normal animals the 

 injection of glucose causes an increase in the carbon-dioxide excretion 

 and a rise in the respiratory quotient, which it will be remembered is 

 a ratio expressing the relationship between the amount of carbon dioxide 

 excreted and of the oxygen retained in the organism. When carbohy- 

 drate is undergoing combustion, the quotient is nearly 1, whereas with 

 that of protein it .is about 0.7 (see page 547). By observing the quotient 

 under given conditions one can compute the proportions of carbohydrate 

 and of fat and protein that are undergoing metabolism. In the hands 

 of Murlin and others, 27 this method has proved of some value in settling 

 certain questions concerning the utilization of glucose in normal and 

 diabetic animals ; but the results must be interpreted with great care on 

 account of the fact that temporary changes in the blood may cause a 

 greater or a less expulsion of carbon dioxide from it. Thus, if acids 

 appear in the blood, they will dislodge carbon dioxide, and apparently 

 cause the respiratory quotient to rise. Alkalies, on the other hand, ap- 

 parently cause the quotient temporarily to fall, and unless the observa- 

 tions are done over a long period of time and with great care, faulty 

 conclusions are very apt to be drawn from the results. 



Diabetes and the Ductless Glands 



We are now in a position to consider the forms of experimental dia- 

 betes produced by disturbances in the ductless glands. 



Relationship of the Pancreas to Sugar Metabolism. In no other of 

 the many causes of diabetes has greater interest been shown than in 

 that due to disturbance in the pancreatic function. Many of the earlier 

 clinicians who followed cases of diabetes mellitus into the postmortem 

 room, noted that definite morbid changes in the pancreas were a fre- 

 quent accompaniment of the disease. Prompted by these observations, 

 several investigators attempted experimental extirpation of the gland, 

 but did not succeed in producing- glycosuria in the few animals that 

 survived the operation. Their failure, no doubt, Avas due to incom- 

 plete extirpation. To reduce the severit}^ of the operation, Claude Ber- 

 nard injected oil into the pancreatic duct, and tied it; but he succeeded 

 in keeping only two dogs alive for any length of time, and these did 

 not exhibit glycosuria. Neither were other investigators that adopted 

 similar methods any more successful. It looked as if the pancreas had 

 very little to do with the cause of diabetes. In the year 1889 Minkowski 



