618 



ELECT HICAL STIMULATION OF THE FROG'S HEART. 



contraction, and in this case latency 

 is reduced. It is to be noted that 

 this induced auricular contraction 

 does not cause another induced ven- 

 tricular systole: its further effects 

 seem to be lost or dissipated. 



At two points in chart T (Fig. 

 213), ventricular systole being ad- 

 vanced half-way and 0*6 of the way to 

 its maximum, the auricular latency 

 is equal, and when at the end of ven- 

 tricular relaxation the auricle con- 

 tracts at the same time as the 

 ventricle, the latency is still about 

 the same. The time lost, therefore, 

 in this case is in ventricular redupli- 

 cation : either the impulse from the 

 auricle is transmitted at different 

 speeds at different times, or it meets 

 at different times with variation in 

 the excitability of the ventricle. 

 The later in the systole the stimu- 

 lation falls the less is the resistance 

 to the transmission of the impulse 

 or the greater the excitability of the 

 ventricle. 



The whole subject of the rhyth- 

 mical contraction of the frog's heart 

 and its stimulation and inhibition 

 is a very complex and difficult one. 

 The points upon which our pi-esent 

 research seems to us to throw some 

 light are the nature and mode of 

 transmission of the stimuli which 

 one cavity transmits to another in 

 the ordinary process of rhythmical 

 contraction. Marey's researches have 

 shown that in the ventricle itself 



