( 597 ) 



is untenable. Mr. Wolterson accordingly gives an alternating expla- 

 nation which, in my opinion possesses sonic probability, and which 

 agrees with Martin's hypothesis on the nature of the vagus action. 



Lei ns suppose thai by the action of the vagus sonic catalytic 

 substance — say Martin's A'-ions - is produced in die receptive 

 substance of the cardiac muscle, then the above slated quantitative 

 relation will be explained, if we may assume that the substance, 

 produced by vagus action, is only to a limited extent soluble in the 

 medium. For with a small production of the catalyser this latter 

 will be dissolved and will increase the retardation, but when the 

 medium has become saturated with the catalyser, further secretion 

 is without effect. It must further be assumed that the newly formed 

 catalyser is at once removed from the substance by diffusion or is 

 deposited in the form of indifferent compound, for the vagus action 

 is known to cease after a short time. Only when the duration of 

 the stimulus is increased and catalytic substance is again and again 

 produced, the disappearance of the catalyser may be compensated 

 and the retardation may be lasting. 



The second chemical process we meet in Mr. Wolterson's thesis, 

 that of the contractility, cannot be submitted to the above followed 

 treatment, since the time-factor is wanting. We tried to introduce 

 this latter by seeking the relation between the intensity of the vagus 

 stimulation and the duration of the inotropic action, but this latter 

 is not itself a chemical reaction, but only a modification of the 

 conditions under which periodically recurring reactions take place. 

 The negative inotropy may at the utmost be regarded as a diminution 

 of the quantity C in the formula tp = kC, which amounts to the 

 assumption that by vagus stimulation the quantity of the just men- 

 tioned substance, undergoing chemical change, is diminished. But 

 this also is uncertain, for in the chemical reaction of the automatism 

 C represents part of Langley's receptive substance, which is different 

 from the contractile substance. So I prefer to keep the two chemism 

 apart and to consider the inotropy entirely by itself. 



Placing ourselves on this point of view, we notice: 1. that with 

 feeble and increasing vagus "stimuli the inotropic effect on the 

 sinns and auricle gradually increases with the intensity of the 

 stimulus, until a certain degree of inotropy has been reached, 

 after which it does not increase further for any intensity of the 

 stimulus; 2. that an analogous relation holds good for the duration 

 of the inotropic effect ; 3. that the pessimum of contractility is found 

 about the end of the first third or fourth part of the total duration, 

 for which the inotropy exists. 



