GALVANIZATION OF THE PNETJMOGASTKICS. 233 



flaccid, and its fibres are for the time paralyzed. The ques- 

 tion then arises whether this action is directly exerted on the 

 heart through the nerves, or whether an influence is conveyed 

 to the nervous centre, and transmitted to the heart in another 

 way. This is settled by the experiment of dividing the 

 nerves and galvanizing alternately the extremities connected 

 with the heart and those connected with the nervous centres. 

 It has been ascertained that galvanization of the extremities 

 connected with the heart arrests its action, while galvaniza- 

 tion of the central extremities has no such effect. Another 

 interesting fact also shows that the influence exerted upon 

 the heart is through the motor filaments of the pnenmogas- 

 trics. It has been shown by Bernard, in a very curious series 

 of experiments which we will not fully discuss in this connec- 

 tion, that the woorara poison paralyzes only the motor nerves, 

 leaving the sensory nerves intact. If we expose the heart 

 and pneumogastric nerves in a warm-blooded animal poi- 

 soned with this agent, and continue the pulsations by keep- 

 ing up artificial respiration, we find that the most powerful 

 current of galvanism passed through the pneumogastrics has 

 no effect upon the heart. The effect of a feeble current of 

 galvanism upon the motor nerves is so like the operation of 

 the natural stimulus, or nervous force, that for a time many 

 physiologists regarded the two forces as identical. Though 

 this view is not received at the present day, it is an admitted 

 fact that by galvanism we imitate in the closest manner the 

 natural action of the motor nerves, and this has become a 

 most valuable means of investigation into the physiology of 

 the nervous system. 



Though galvanization of the pneumogastrics arrests the 

 action of the heart in nearly all animals, there are some in 

 which this does not take place, as in birds ; a fact which is 

 stated by Bernard, 1 but for which he offers no explanation. 

 In some experiments instituted on this subject a few years 



1 BERNARD, Physiologie et Pathologic da, Systeme Nerveux,Psiris, 1858, tome ii., 

 p. 394. 



