THE RELATION OF THE HEART-BEAT TO ELECTROLYTES. 185 



111 the ray heart, for instance, a concentration of •000001 M to 

 •00001 M of Ce • • * or Nd • • • is sufficient to cause prompt arrest 

 in diastole. The same ei!ect can be produced by Mg • •, but the 

 concentration needed is about '02 M. If our explanation of the 

 action of magnesium on the heart is true, it should of course be 

 found that the dose of Mg needed to arrest the heart depends greatly 

 on the P + of the solution in which it is applied. An increase in the 



H 

 numerical value of the P+ should tend to counterbalance the effect 



H 

 of magnesium. This is abundantly confirmed by experiment. For 

 example : a ray heart was brought to rest by raising the concentration 

 of Mg • • in the solution, perfusing it to ^025 M, The diastolic 

 arrest occurred after two or three contractions. When the heart had 

 remained completely at rest for a minute with this solution running 

 through, without changing the concentration of Mg • • the P + of 



H 

 the solution was raised from about 6^5 to 9. Within a few seconds the 

 heart started beating, and continued to beat in this solution as strongly 

 and regularly as in the original solution which contained no excess 

 of Mg--. 



Consideration of the relations of colloidal materials to simjjle and com- 

 plex trivalcnt JMtions enables us to make certain inferences as to the natiire 

 of these colloidal suhsta7iees from which we can predict their relations to 

 certain other ions. Applying this lyrinciple to the heart, ive arrive at 

 conclusions c(s to the nature of the colloidal membranes in its structure 

 from which un can predict the action of magnesium upon the heart-beat. 



Finally, I wish to indicate certain directions in which experiments 

 of this kind may assist in the development of a scientific comparative 

 physiology. 



Two instances which I have encountered in the course of work at 

 the Plymouth Laboratory this summer may serve as illustrations.* 



The facts already stated about the general similarity in the re- 

 lations of the heart muscle of widely different species to Ca, Sr, 

 and Ba encourage the belief that the general character of the 

 mechanism is the same in these varieties of heart muscle. Can we 

 find differences in the relations of the membranes to " charging " 

 electrolytes ? What kind of differences are to be looked for ? 



A study of the properties of colloids by a variety of methods leads 

 to tlie following conclusions with respect to the part played by the 



* I am much indebteil to Miss Dale, of Xewnham College, for her skilful assistance in 

 this work. 



NEW SKRIES.— VOL. IX. NO. 2. OCTOBEU, 1911. N 



