78 LECTURE V. 



The question now arises as to what the connection is between the 

 " diabetic puncture " and the flooding of the organism with sugar. Claude 

 Bernard, by means of the following experiment, showed that the vagus 

 nerves participate in this. 1 If the " diabetic puncture " is performed 

 after cutting these nerves at the neck, it is as effective as when the nerves 

 remained intact. On stimulating the peripheric stumps of a vagus nerve, 

 no glucosuria ensues. It appears immediately, however, if the central end, 

 i.e., the end connected with the medulla oblongata, is stimulated. In 

 such experiments Bernard showed that the whole body of the animal 

 experimented upon was flooded with sugar. The greatest quantity was 

 found in the hepatic veins. Bernard showed, furthermore, that cutting 

 the vagus nerves at the neck resulted in making the liver free from sugar. 

 He concludes from all these experiments that in the medulla oblongata 

 there is a center which regulates the transformation of sugar by the liver. 

 Communication, i.e., the excitement, is provided by means of the vagus 

 nerve. The sugar formation caused by stimulation of the central stump 

 of the vagi nerve, Bernard conceives to be a reflex action; 2 and it is the 

 pulmonary branches of the vagus which contain the fibers acting upon 

 the sugar center, for if the vagi are cut above the liver and below the 

 lungs, no influence upon the sugar formation of the liver was observed. 



Now how does this sugar center exert its influence upon the liver? 

 Bernard cut through the spinal cord at different places below the medulla 

 oblongata, and found that the path of communication must lie in the 

 upper parts of the spinal cord; for if it was severed below the lower dorsal 

 vertebrae, the sugar formation in the liver was not affected. C. Eckhard, 3 

 who confirmed this conclusion, found that after severing both the vagi 

 and sympathetic nerves in the neck, a successful diabetic puncture could 

 be made. After severing the splanchnic nerves, however, it ceased to be 

 operative. This indicates that the diabetic puncture acts upon the trans- 

 formation of the carbohydrates in the liver by nerve impluses passing 

 along the path of the splanchnic nerves. 



We must assume, therefore, that the sugar formation in the liver is 

 regulated directly by a center in the medulla oblongata. The vagi nerves 

 conduct the centripetal impulses, and the splanchnic nerves the centri- 

 fugal. Later on, when we come to discuss digestion, and especially 

 the dependence of the secretion of the digestive glands upon certain 

 nervous influences, the above hypothesis will no longer appeal to us as 

 remarkable. 



Thus far we have left the matter unsettled as to whether the liver alone 

 gives up sugar after the "diabetic puncture," or whether the sugar in the 



1 Cf. C. Eckhard: Beit. Anat. Physiol. 8, 77 (1879). 



2 Cf. E. F. Pfliiger: Das Glykogen, loc. cit. 386. 



3 Beitr. Anat. Physiol. 4, 138. 



