INTERNAL SECRETION 



375 



line and without sugar. In one or two hours after the operation, the 

 urine will have become clear and acid, and it will react readily with any 

 of the copper tests. When this operation is performed without injuring 

 the adjacent organs, the presence of sugar in the urine is temporary; 

 and the next day the secretion will have returned to its normal condition. 

 The production of glycosuria in this way, in animals, is important in its 

 relations to certain cases of diabetes in the human subject, in which 

 the affection is traumatic and directly attributable to injury near the 

 bulb. The irritation is not conveyed through the pneumogastric 

 nerves, for the experiment succeeds after both of these nerves have been 

 divided ; nevertheless, the pneumogastrics have an important influence 

 on glycogenesis. If both nerves are divided in the neck, in a few hours 

 or days, depending on the length of time that the animal survives the 

 operation, no sugar is to be found in the liver, and there is reason to 

 believe that the glycogenic action has been arrested. After division of 

 the nerves in the neck, stimulation of their peripheral ends does not 

 affect the production of sugar ; but stimulation of the central ends pro- 

 duces an impression that is conveyed to the nerve-centre, is reflected to 

 the liver and gives rise to an increased production of sugar. It reaches 

 the liver probably through the sympathetic system. 



It has been observed that the inhalation of anesthetics and irritat- 

 ing vapors produces temporary glycosuria; and this has been attributed 

 to an irritation conveyed by the pneumogastrics to the nerve-centre, 

 and reflected, in the form of a stimulus, to the liver. It is for this 

 reason that the administration of anesthetics should be avoided in 

 experiments on glycogenic action. 



In addition to the varied uses of the liver that have been described, 

 it is thought that this organ either arrests or in some way influences the 

 condition of certain foreign and poisonous substances absorbed from 

 the alimentary canal ; but a study of this action does not properly 

 belong to physiology. 



DUCTLESS GLANDS AND INTERNAL SECRETION 



Certain organs in the body, with a structure resembling, in some 

 respects, the true glands, but without excretory ducts, have long been 

 the subject of physiological speculation ; and the most extravagant 

 notions concerning their uses prevailed in the early history of physi- 

 ology. The discovery of the action of the liver in modifying the com- 

 position of the blood passing through its substance foreshadowed the 

 probable mode of action of the ductless glands ; for so far as the pro- 

 duction of glycogen is concerned, the liver belongs to this class. Indeed, 



