421 



cologist saw, that the second heart often showed slower contractions. 

 Experiments witli the sympathetic nerve gave analogous results. 



Now the purpose of our experiments was in the lirst place to 

 control the results of LoKWi's researches under more physiological 

 conditions. 



In the vena cava of a frog A a glass tube is inserted and in 

 this way a suitable saltsolution is conducted through the heart. A 

 similai' small tube is introduced into the aorta. Then we see, that 

 the saltsolution will leave the heart in a rhythmical manner. If 

 then the fluid, leaving the heart, is led to the vena cava of another 

 frog B, the fluid will run through the heart B, and after leaving 

 it by the aorta of this second frog, it may be taken up again by 

 the vena cava of the first frog A. Thus we obtain a circulation of 

 saltsolution through both frog'^; hearts. This method of socalled 

 "crossing circulation" was first introduced by Prof. J. C. Hemmeter. 



Now, if the sympathetic of the first frog A be .stimulated electric- 

 ally, causing acceleration of the heart beat of this frog, it can be 

 observed that already after a few seconds, the heart rale of the 

 second frog B is also quickened, although the sympathetic of this 

 animal has not been stimulated. How to account for the acceleration 

 of the second heart? Evidently in no other way than by assuming 

 that in the first heart A, in virtue of permeability of course, sub- 

 stances were liberated which had a similar effect upon the second 

 heart as if this had been directly stimulated. I shall presently come 

 back to the probable nature of these substances. 



How it is possible that substances, liberated by a physiological 

 action of an organ, here the heart of the frog A, may also stimulate 

 the same organ of the second animal B, I shall not discuss here. 

 It is suflTicient to say, that there is an analogy between this case 

 and the secretion of saliva. If we allow a salt solution to percolate 

 through the salivary gland, as J. Demoor has demonstrated some 

 years ago, no saliva is secreted. However it does occur if u small 

 quantity of saliva is added to the saltsolution. The product formed 

 during the activity of the salivary gland is, it seems, a stimulus 

 again to further secretion of saliva. The substances, formed in the 

 stomach during conversion of protein, excite gastric secretion. It is 

 therefore not strange that the substances, liberated in the first heart 

 during stimulation of the sympathetic, should have a stimulating 

 action on the second heart. 



Dr. Brinkman and Miss van Dam made yet another experiment 

 that in a still more convincing and striking manner demonstrates, 

 that the transmission of stimuli can take place by means of fluids, 



