I 



MODE OF ACTION ON THE VAGUS. 505 



The thorax was then opened, and the heart found beating ; 

 resph'atory movements recommenced on opening the thorax. 



The bladder was found greatly distended ; there had been 

 micturition during the experiment, which was probably only 

 overflow. 



Remarks. 



We append a diagram (p. 518) showing the coincident varia- 

 tions of blood-pressure and secretion of urine, which will be 

 more fully commented on later. {Vide effect on urinary 

 secretion.) 



So far as the phenomena of circulation are concerned, this 

 experiment shows that while a small dose of casca slows the 

 pulse, an additional one greatly quickens it. This action of 

 casca closely resembles the effect of digitalis, which first slows 

 the pulse by stimulating the vagus-roots, and then quickens it 

 by paralyzing the ends of the vagus in the heart. It therefore 

 seemed probable that the cardiac ends of the vagus would be 

 found to be paralyzed by large doses of casca. 



It was possible that the primary slowing of the heart's action 

 might be due to stimulation of the inhibitory apparatus in the 

 heart itself, and not to the action of the drug on the vagus- 

 roots. Two questions, therefore, were to be settled : — 



1st. Is the primary slowing of the pulse due to stimulation 

 of the vagus-roots, or to stimulation of the inhibitory apparatus 

 in the heart ? 



2nd. Is the secondary acceleration of the pulse due to 

 paralysis of the ends of the vagus in the heart ? 



To answer these questions the following experiments were 

 performed {vide antea, p. 297) : — 



Experiment XXXIV.— March 21. 



Action on the Heart and Arterial Pressure of a small dose of 



Casca. 



A dog weighing 8 lb. was chloroformed, and kept under 

 chloroform during the experiment. 



A. cannula was inserted into the right carotid and into the 

 right femoral vein. 



