COOLED HEMIT-STIMULATION OF VENOUS SINUS. 



605 



equal or of very slightly differing values. Thus in a heart much 

 cooled (D 1 and 2 Fig. 196) we have towards the commence- 

 ment of ventricular systole and towards the end of relaxation 

 a latency for the induced ventricular beat of l"-2. 



Venous Sinus. 



In the heart which has been moderately or slightly cooled, 

 4 — 6^ C, the occurrence of ventricular reduplication without a 

 precedent auricular reduplication is very rare, even when strong 

 stimulation is employed. The refractory period occasionally 

 observed may disappear after a few stimulations have been 

 given, or it may persist. Furthermore, on cooling a heart which 

 has at a certain temperature, E^ (Fig. 197), shown a refractory 

 period, we may find this converted into a period during which 

 stimulation causes an omission of the following beat. Eg. 



Fig. 197. 



E,. 



E^. 



Ki to Ej. Levers as in A, but no auricular tracing given. Stimulation of 

 Venous Sinus. Ei, before cooling ; E2, after cooling. 



The duration of the diastolic pause is markedly influenced by 

 temperature, whereas it appears to be but slightly affected by 

 variation in the instant of stimulation by which it is produced. 



