412 



USES OF THE LIVER-DUCTLESS GLANDS. 



tion 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 diabetes in this way, in animals, 

 is important in its relations to certain cases of the disease in the human 

 subject, in which the affection is traumatic and directly attributable to injury 

 near the medulla. Its mechanism is difficult to explain. The irritation is 

 not propagated through the pneumogastric nerves, for the experiment suc- 

 ceeds after both of these nerves have been divided ; nevertheless, the pneumo- 

 gastrics have an important influence upon glycogenesis. If both of these 

 nerves be divided in the neck, in a few hours or days, depending upon 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 periph- 

 eral ends does not affect the production of sugar ; but stimulation of the cen- 

 tral ends produces an impression which is conveyed to the nervous centre, is 

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



"With regard to 

 the influence of the 

 sympathetic nerves 

 upon glycogenic 

 action, there have 

 been few if any ex- 

 periments which 

 lead to conclusions 

 of any great value. 

 It has been ob- 

 served that the in- 

 halation of anaes- 

 thetics and irrita- 

 ting vapors pro- 

 duces temporary 

 diabetes ; and this 

 has been attributed 

 to an irritation con- 

 veyed by the 



FIG. 138. Section of the head of a rabbit, showing the operation of punct 



uring the floor of the fourth ventricle (Bernard). 

 a, cerebellum : b, origin of the seventh pair of nerves ; c, spinal cord ; 



, , , 



prigin of the pneumogastric ; e, opening of entrance of the instrument . 



into the cranial cavity ; /, instrument ; g, fifth pair of nerves ; h, audi- mOSfastricS to the 

 tory canal ; /, extremity of the instrument upon the spinal cord, after it 

 has penetrated the cerebellum ; k, occipital venous sinus ; Z, tubercula 

 quadrigemina ; m, cerebrum ; n, section of the atlas. 



nerve-centre, and 

 reflected, in the 



form of a stimulus, to the liver. It is for this reason that the administration of 

 anaesthetics should be avoided in all accurate experiments on glycogenic action. 



The following summary expresses what is known with regard to the pro- 

 duction of glycogen by the liver and its conversion into sugar : 



A substance exists in the healthy liver, which is readily convertible into 

 sugar; and inasmuch as this is changed into sugar during life, the sugar 

 being washed away by the blood passing through the liver, it is proper to 

 call it glycogen, or sugar-forming matter. 



