V ABLATIONS IN THE GLYCOGENIO FUNCTION. 



471 



traumatic and directly attributable to injury near the medulla. Its mechanism is dif- 

 ficult to explain. The irritation is not propagated through the pneumogastric nerves, 

 for the experiment succeeds after both of these nerves have been divided; but the 

 influence of the pneumogastrics upon glycogenesis is curious and interesting. 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 function has been arrested. After divi- 

 sion of the nerves in this situation, galvanization of their peripheral ends does not affect 

 the production of sugar ; but, by galvanization of the central ends, an impression is con- 

 veyed to the nervous centre, which is reflected to the liver and produces a hypersecretion 

 of sugar. These questions will be referred to again, in connection with the physiology 

 of the nervous system. 



FIG. 141. Section of the head of a rabbit, showing the operation of puncturing the floor of the fourth ventricle, 



(Bernard.) 



a, cerebellum ; &, origin of the seventh pair of nerves ; c, spinal cord ; d, origin of the pneumogastric; e, opening of 

 entrance of the instrument into the cranial cavity ; /, instrument ; g, fifth pair of nerves ; A, auditory canal : ', 

 extremity of the instrument upon the spinal cord after having penetrated the cerebellum ; k, occipital venous 

 sinus ; Z, tubercula quadrigemiua ; m, cerebrum ; n } section of the atlas. 



With regard to the influence of the sympathetic system upon the glycogenic function, 

 there have been few if any experiments which lead to conclusions of any great value. 



It has been observed that the inhalation of anaesthetics and irritating vapors produces 

 temporary diabetes ; and this has been attributed to an irritation conveyed by the pneu- 

 mogastrics to the nerve-centre, and reflected, in the form of a stimulus, to the liver. It 

 is for this reason that we should avoid the administration of anaesthetics in all accurate 

 experiments on the glycogenic function. 



Destination of Sugar. Although sugar is constantly produced by the liver and taken 

 up by the circulation, it is exceptional to find it in the blood after it has passed through 

 the lungs. It is difficult to ascertain the precise mode of its destruction in the lungs, and, 

 indeed, the nutritive function of sugar in the economy is not thoroughly understood. All 

 that we can say of the destination of liver-sugar is, that it probably has the same office 

 in nutrition as the sugar taken as food and that resulting from the digestion of amylaceous 

 matters. The facts bearing upon this question will be reviewed under the head of nutri- 

 tion. 



