THE PERMEABILITY OF MEMBRANES 143 



Conclusions of the same kind are drawn by Straub (1912, p. 14) with regard to 

 the action of calcium on the heart muscle, which is impermeable to this substance 

 big. 46 illustrates this point. In the tracing, the first three beats are under the 

 action of Ringer's solution containing sodium, potassium, and calcium. At the 

 signal, the solution is suddenly changed for a similar one without calcium. It is 

 seen how the want of calcium is shown in the first beat succeeding the change. 

 At the end of the signal, the normal Ringer's solution is replaced, with its action 

 on the very next beat. Straub reckons that the effect must be manifested in less 

 than 0-1 second. It is to be remembered that the interior of the cells contain 

 calcium, which could not diffuse out by the time at which the action of a calcium- 

 free solution is manifest. The calcium could merely be removed from the outer 

 surface of the cells. 



The experiments of the same investigator on the effect of muscarine on the 

 heart of Aplysia (1907) have already been described. When this organ is allowed 

 to lie in a small quantity of a solution of the drug, it is noticed that the effects 



FIG. 46. EFFECT ON THE FROG'S HEART OF DEPRIVA- 

 TION OF CALCIUM. The first three beats are 

 normal in Ringer's solution (which contains 

 calcium). At the beginning of the white space, 

 this solution is suddenly changed for one other- 

 wise similar, but from which the calcium has 

 been omitted. The effect is shown at once on 

 the first beat after the change. At the end of 

 the white space, the normal solution is replaced, 

 with an immediate effect. Time in seconds. 

 Note that less than O'l second is required to 

 affect the muscle cells, so that the action must 

 be exerted on the colloidal system of the cell 

 membrane. This is the only part of the cell 

 which could be deprived of calcium with such 

 rapidity. 



(Straub.) 



of the poison are only seen while there is a particular concentration of it left 

 in the solution ; the heart then recovers, although it is found that muscarine 

 has been stored inside its cells and remains there. It is plain that the effect 

 was only to be seen while the poison was in the act of passing through the 

 membrane, so that it must be supposed that it leaves the membrane, and passes 

 into the cell substance as soon as there is less than a certain minimal concentra- 

 tion in the outer liquid. 



Somewhat similar results were obtained by Neukirch (1912) with the action 

 of pilocarpine on the excised small intestine of the rabbit, immersed in warm 

 oxygenated saline solution. The addition of pilocarpine to this solution causes 

 a great increase of tonus, which slowly decreases but does not disappear, even 

 in several hours. But, if the pilocarpine solution be changed for fresh saline, 

 a second increase of tonus occurs as the alkaloid diffuses out from the cells into 

 the saline. A remarkable fact is that if, as soon as this tonus has developed, the 

 pure saline be exchanged for the original pilocarpine saline, so that diffusion 

 ceases on account of equality of concentration inside and outside of the cells, the 

 tonus also disappears. It seems, then, that in this case, the actual presence of 



