( 592 ) 



For (lie automatism it seems to me to be settled, that it must be 

 based on chemical processes. 



For the remaining cardiac properties: conductivity, local sensitiveness 

 to stimuli, contractile power and tonicity the decision is more 

 difficult. The law of van 't Hoff-Arrhenius concerning the relation 

 between reaction-velocity and temperature can only be applied if 

 the duration of the reaction is known. Now the velocity of conduc- 

 tion, measured with this purpose, increases with temperature up to 

 a certain optimum l ) whereas correspondingly the duration of the 

 contractions is diminished 3 ). The local excitability, however, has 

 not been studied yet from this point of view, while also for the 

 contractile power the time factor is still lacking. But the contraction 

 of a muscle and also that of the cardiac muscle is so universally 

 considered a truly chemical process, that the reader will not object 

 to classing it among chemical phenomena without further arguments. 

 As lo the tonicity we are absolutely in the dark, although we know 

 that rise of temperature chiefly brings about a change, in which 

 the tonus is definitely abolished. 



In preparing his thesis Mr. Wolterson had chiefly to deal with : 



1. changes in the automatism (chronotropy) ; 



2. changes in ihe contractile power (inotropy). 



Both these changes are purely chemical phenomena, as was shown 

 above. 



For chemical processes the law of GüLDBERG and Waage holds 3 ], 

 and we may apply this law to the processes here dealt with. For 

 this purpose we shall have to give a nearer definition for our special 

 case of the conception "times of equal change". 



By "times of equal change" we mean the times in which a defi- 

 nite reaction has taken place between two accurately fixed and in 

 the corresponding cases analogous terminal points. The total duration 

 of a cardiac period is such a characteristic time element, the begin- 

 ning and end of which cannot be determined with the balance after 

 chemical analysis, but still are determined by biological characteris- 

 tics. The time between the beginning and the end of a cardiac 

 period may be looked upon as a time of equal change provided no 



!) Th. W. Engelmann. Onderz. Physiol. Lab. Utrecht (3d series) III p. 98. Above 

 the optimum the conductive velocity diminishes again. 



2 ) Hofmann I.e. p. 247. Recently confirmed by V. E. Nierstrasz; vide acad. thesis, 

 Utrecht 1907, p. 145, fig. 22 : a fall in temperature of 9° gave an increase of 

 the duration of the systole to the double value. 



3 ) E. Cohen. Ned. Tijdschr. v. Geneesk. 1901, Vol. I, p. 58. Cf. also Zwaardemaker, 

 ibidem, 1906. Vol. II. p. 868. 



