212 



Prof. J. A. Mc William. 



[May 17, 



fluttering appearance ; the ventricles beat much more rapidly than 

 before, though they do not keep pace with the auricles. 



On the other hand, stimulation of the inhibitory area, while it 

 causes a rapid fluttering action of the auricles, induces either a very 

 marked slowing, or a complete standstill in the ventricles. This 

 result is a mixed one — ventricular inhibition, resulting from stimula- 

 tion of certain structures in the inhibitory area, and auricular accelera- 

 tion, in all probability due to an escape of the stimulating current to 

 the excitable auricular tissue. 



The inhibitory effects on the ventricle much resemble those 

 caused by vagus stimulation. There is depression of the ventricular 

 contraction force, and changes in the shape and duration of the ven- 

 tricular curves similar to those occurring under vagus influence. 

 Stimulation of the inhibitory area and of the vagus are both rendered 

 ineffective by the administration of atropine. 



But there are certain points of difference : — 



(1.) The strength of current necessary to inhibit the ventricles is 

 very much less when the current is applied to the inhibitory area 

 than when it is applied to the vagus. 



(2.) Stimulation of the inhibitory area remains effective in arrest- 

 ing the ventricular action, after curare nas been administered in such 

 amount as to cause stimulation of one or both vagi in the neck to be 

 entirely without inhibitory result. 



(3.) In many instances when the vagi have become exhausted, or 

 have lost their inhibitory power from less definite causes, the inhibitory 

 area remains effective. 



It seems clear from the very different relation borne by the inhibi- 

 tory area to certain poisons, to the strength of stimulating current 

 necessary, to exhaustion, &c, that in exciting this area we are dealing 

 with structures of a more or less special nature, differing markedly 

 in their character from the ordinary inhibitory fibres running in the 

 trunks of the vagus nerves. 



The important structures of the inhibitory area pre situated super- 

 ficially; they may be readily paralysed by the application of a few 

 drops of a 4? per cent, solution of cocaine hydrochlorate, or of strong 

 ammonia. 



The region in question does not contain a motor centre for the 

 heart muscle. Destruction of this area does not arrest the spontaneous 

 rhythm of the organ (which indeed originates in parts some distance 

 removed from the inhibitory area, viz., in the ostial parts of the great 

 veins, especially the vena cava superior and the pulmonary veins), 

 i^or is the propagation of the contraction from one part of the heart 

 to another in any way deranged or interfered with. 



The inhibitory area probably contains structures to which many at 



