ACTION OF THE EXCISED MAMMALIAN HEART. 
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the important one was shown, 1st, by placing the heart in a constant temperature 
chamber at 40°, 2nd, by placing it in a chamber surrounded by ice. In the first case 
the characteristic prolongation was almost entirely absent, in the second it was greatly 
exaggerated. (Tracing 6.) 
Tracing 6. 
Beats of Dog’s heart in warm chamber at 38° C.; the decline is rapid and there is no appreciable 
prolongation of the ventricular contraction. 
Tracing 7. 
Effect of cold (8° C.) on ventricular contraction of a Kitten’s heart; the latent period is about 
- 5 second, the duration of contraction is at least 10 seconds (this is the greatest prolongation 
that we have observed). 
We do not think, however, that the temperature is the only condition involved, 
though it is certainly the chief one, for we have, as a rare exception, observed an 
alternately longer and shorter contraction, without of course any possible alternation of 
temperature, and we have found that the hearts of very young animals are more 
susceptible of this modification than those of fully grown animals. (Tracing 7.) An 
example of the excessive prolongation of which the contraction is capable under the 
influence of low temperature is furnished by Tracing 8. 
In the course of our experiments regarding the effect of temperature upon the 
heart’s contraction, we made observations showing the great susceptibility of the 
Mammalian heart to cold, and the preservative influence of cold upon its capacity for 
action. The effects of cold (surrounding by melting ice) are, in the order in which 
