25 
often such an injection of caffeine was fol- 
lowed by a decrease in the completeness of 
systole. In other cases there was a mo- 
mentary slight increase in strength followed 
by a short decrease immediately following 
the caffeine injection. This is illustrated by 
figure 4. 
No increase in heart rate was observed fol- 
lowing the injection of acetanilide in the 
doses used in these experiments. On the 
other hand, there was generally a decrease of 
from 10 to 20 beats per minute, the slowing 
evidently being due to a direct action on the 
heart muscle, since paralysis of the vagi by 
atropine did not prevent it. As regards the 
rate, caffeine proved to be completely antago- 
nistic, when injected at the same time usually 
preventing any slowing and when injected 
subsequent to an injection of acetanilide 
causing the heart rate to return at once to 
the normal or in some cases to a rate more 
rapid than normal. 
There is a marked fall in blood pressure im- 
mediately following the injection of acetani- 
lide, which is probably due in a great measure 
to the lessened efficiency of the heart. The m- 
jectionof caffeine, although restoring the rate 
to normal, has hardly any effect upon the 
blood-pressure curve after injections of ace- 
tanilide. In general, there is a slight up- 
ward tendency, but in certain instances caf- 
feine seemed to check the return to normal, 
agreeing in this respect to the occasional ten- 
dency of caffeine to lessen the completeness of 
the heart’s contraction. Figure 5 illustrates 
the lack of antagonism between caffeine and 
acetanilide upon the blood pressure. 
Sodium bicarbonate was used to antagonize 
the action of acetanilide only after the heart 
had become seriously poisoned. The immedi- 
ate effect of large doses (2 grams) was to 
slightly increase the depression as marked by 
the systolic phase. This was quickly fol- 
lowed, however, by a rather marked and 
prolonged increase in the contractile power of 
the ventricle, as is shown by the nearer ap- 
proach of the writing lever to the base line 
Fig. 5.— Blood pressure tracing taken from tlie carotid of dog. Note especially the secondary fall immediately following the injection of 0.075 gram call’eine citrate. 0.500 gram 
acetanilide injected at A. 
