VASO-MOTOR NERVES 39 



"No less pregnant of future discoveries," says this biographer,, 

 "was the idea suggested by this newly found-out action of the hepatic) 

 tissue, the idea happily formulated by Bernard aa /internal secretion.'' 

 No part of physiology is at the present day being more fruitfully 

 studied than that which deals with the changes the blood undergoes 

 as it sweeps through the several tissues." The study of these in- 

 ternal secretions constitutes a path of inquiry which has within re- 

 cent years been pursued with conspicuous success. 



To Bernard we owe the discovery of the remarkable fact that 

 temporary diabetes may be caused by puncture of the fourth ven- 

 tricle. This glycosuria was formerly attributed to direct stimula- 

 tion of the liver through its nervous connections. It has been found. 

 however, that if the left adrenal is cut off from the left sympathetic 

 nerve, no sugar appears in the urine after the medulla has been punc- 

 tured, and it is now believed that the stimulus is transmitted by the 

 left sympathetic nerve to the left adrenal, whence it is passed to the 

 right adrenal by the connecting nerves. As a consequence of the 

 medullary puncture the adrenals secrete more actively and the in- 

 creased flow of the adrenal secretion in its turn brings about an 

 excessive output of sugar by the liver.* A number of toxic influences 

 possibly act in the same way, the glycosuria to which they give rise 

 being partly the result of the action they exert on the diabetic center 

 in the medulla, and partly an effect of their stimulating action on the 

 sympathetic nerves, or on the adrenals directly, thus, in any case, 

 causing hyperfunction of the chromaffin system, with consequent 

 overproduction of sugar by the liver. 



Discovery of Vaso-Motor Nerves — Next in importance to the dis- 

 covery of glycogen was Bernard's discovery of the vaso-motor 

 nerves. "To Claude Bernard," says Sir Michael Foster, "we owe the 

 foundations of the vaso-motor system. He made known to us the ex- 

 istence of vaso-motor nerves and he also made known to us that vaso- 

 motor nerves are of two kinds, vaso-constrictor and vaso-dilator — ^the 

 two fundamental facts of vaso-motor physiology." The importance 

 of this discovery can hardly be over-estimated when we consider that 

 there is scarcely a physiological problem of any magnitude which does 

 not sooner or later involve vaso-motor questions. The vaso-motor 

 nerves presiding as they do over the contraction and dilation of the 

 walls of the blood vessels, assume an important role in such functions 

 as gastric digestion, blood pressure, heat processes, blushing and 

 various other congestions, or on the other hand, the significant blanch- 

 ing of an organ as in sudden fright. 



■^ ' Among Bernard's minor investigations which might be mentioned 

 is that, into the physiological action of curare, a black resenoid ex- 

 tract prepared by the South American Indians from the bark of strych- 

 nos toxifera and used to poison arrows. Owing to its poor diffusi- 

 bility through animal membranes curare i^ harmless taken into the 

 alimentary canal, though the minutest quantity introduced into a 

 wound is fatal., Since Bernard's time curare has become an instru- 

 ment in the hands of the physiologist to enable him to abolish tempo- 

 rarily the movements of the skeletal muscles, enabling him to carry 

 out experiments which could not be made without such aid. 



The precise action of carbonmonoxide gas in asphyxia no one 

 understood until Bernard investigated the matter. His experiments 



♦Futcher Journal A, M. A. Decemher 21, 1912. 



