284 Dr W: H. Gaskell, On certain points [Nov. 27, 



the heart beat with regularity when it was previously irregular ; 

 although it reduces the force of the contractions, yet its ultimate 

 effect is to improve and sustain the contraction force ; although 

 it may diminish the conduction power yet in the end it completely 

 repairs that power. 



The vagus then is essentially the trophic nerve of the heart. 



In endeavouring to proceed further and to find out the nature 

 of this trophic action, it is necessary first to draw attention to 

 certain differences iu the behaviour of the hearts of the frog and 

 the tortoise when the vagus nerve is stimulated. 



In the frog standstill of the auricles and ventricle may be 

 caused by the vagus in three ways, 



1. By cessation of the rhythm. 



2. By diminution of the contractions to the null point, with- 

 out affecting the rhythm. 



3. By the prevention of the passage of the contraction- wave 

 from the sinus to the auricles. 



In the tortoise, standstill is produced by the first and third 

 methods, never as far as I have seen by the second. 



In the frog, the force of the contractions of both auricles and 

 ventricle are affected in a similar manner. In the tortoise the 

 ventricular contractions are absolutely unaffected, while the auri- 

 cular resemble those of the frog in their behaviour to va<ms 

 stimulation. 



This absolute indifference displayed by the ventricle of the 

 tortoise to the influence of the vagus is so striking and unexpected 

 that I have especially endeavoured to find out the meaning of it. 

 Thus it was possible that the coronary system possessed by the 

 ventricle might play the chief part in regulating the force of the 

 ventricular contractions and that the vagus might act on that 

 system. 



I therefore left the heart in the body with blood flow intact, 

 and in the same way as in the suspended heart fixed a point 

 between auricles and ventricle by fastening the outer surface of 

 the base of the aorta to a rigid vertical rod, a ligature attached 

 to the apex of the ventricle was made by a simple contrivance to 

 move a lever up and down without disturbing the natural position 

 of the heart. I found, however, in this case as well as in the 

 case of the suspended empty heart, that the force of the ventri- 

 cular contractions was not influenced by the vagus. In addition 

 to this experiment I caused an artificial blood solution to flow 

 steadily through the coronary system by means of a cannula 

 fixed in the aorta, but with no better success ; all I found was, 

 that the force of the contractions varied directly as the pressure 

 in the coronary vessels, but there was no evidence that the vagus 

 possessed any influence on that force. 



