216 GENERAL ZOOLOGY 



patients suffering from diabetes mellitus. That the symptoms 

 in the case of the depancreatized dog are due to the loss of the 

 islet cells is shown by the fact that the destruction of the alveolar 

 cells alone does not produce them. This can be done by tying 

 off the pancreatic ducts, which causes the degeneration of the 

 alveoli but does not affect the islet cells. Then, too, there is the 

 additional observation that lesions in the islet cells have been 

 found in cases of diabetes mellitus. 



Insulin is an extract prepared from islet cells which when 

 injected into diabetic dogs or diabetic patients alleviates the 

 symptoms. Injection of too much insulin into a normal rabbit 

 produces a rapid fall in blood sugar to about 0.045 per cent, when 

 convulsive seizures occur. These promptly disappear if glucose 

 is injected. Obviously the function of insulin is concerned with 

 the metabolism of sugar, though how it is brought about remains 

 an open question. In general terms, insulin has the property of 

 making dextrose available to tissues so that it may be oxidized. 



Glycosuria and hyperglycemia can be produced in normal 

 animals by injecting extracts of the anterior pituitary gland. 

 The same symptoms often accompany acromegaly. Therefore 

 the anterior pituitary gland produces a hormone which has the 

 power to increase the amount of sugar in the blood. When 

 insulin is absent, as in pancreatic diabetes, the sugar continues to 

 rise in the blood as a result of the continued action of this hor- 

 mone of the anterior pituitary which is known as the diabetogenic 

 hormone. If the anterior pituitary is removed from a depan- 

 creatized clog, glycosuria and hyperglycemia are greatly reduced 

 and the animal may survive for months, at any rate much longer 

 than if its anterior lobe had remained in place. In a sense, then, 

 the diabetogenic hormone is antagonistic to insulin, and this 

 might also be said to be true of epinephrine and of thyroxine. 

 The diabetogenic hormone is antagonistic to insulin in that the 

 former tends to increase the sugar in the blood by promoting 

 glycogenosis, while the latter is active in consuming sugar. 

 The action of epinephrine and thyroxine resembles that of the 

 diabetogenic hormone in their power to increase the sugar in 

 the blood. 



Gonads. — Internal secretions of the gonads are necessary for 

 the full development of secondary sexual characters, which are 

 characters aside from the gonads that distinguish males and 



