EFFECT OF CAFFEINE UPON THE HEART 



143 



affect the ventricles and inhibit them. The ventricles therefore are 

 much less under the influence of the vagus than the auricles. 



The method is of considerable value in that it offers a convenient 

 method of observing the direct action of drugs upon the heart. As an 

 instance of this we may record the effect of an injection of caffeine 

 citrate into a vein. The external jugular vein is exposed and the 

 injection made in the manner described on p. 181. Fig. 113 shows the 

 result of injecting 1 c.c. of a 4 per cent, solution of caffeine citrate in 

 1 per cent, sodium chloride solution into the external jugular of a cat. 

 The solution was previously warmed to body temperature. It is seen 

 that there is an almost instantaneous effect upon both auricle and 



Fig. 113. — Eesult of the Injection of 1 c.c. of a 4 pee cent. Solution 

 of Caffeine Citrate. Tracing reduced to Half Size. 



ventricle, but more markedly on the auricle. The rate remains prac- 

 tically unaltered, but the force is considerably diminished. Afterwards 

 there is a gradual recovery, which is fairly rapid in the case of the 

 ventricle, but slower in the case of the auricle. If the heart be 

 watched during the action of the drug, it is observed that the right 

 auricle becomes greatly distended with blood. If larger doses be 

 injected the effect becomes much more pronounced, and soon affects 

 the ventricle quite as much as the auricle and in the same direction. 

 The right auricle becomes very distended and its movements greatly 

 impeded. "With about 5 c.c. of the solution there is very frequently no 

 recovery of the beat, and the animal dies. 



The effect of other drugs should also be tested. Digitalin is found 



