841 
insignificant. Still, the two are not identical. On the contrary, phy- 
sically corpuscular raying differs fundamentally from light-rays. 
Nor have we succeeded, in spite of strenuous efforts, not even by 
means of the most concentrated visible or ultraviolet light, in 
achieving a recovery of automaticity in an organ perfused with a 
potassium-free fluid. As regards the temperature-coefticient the ana- 
logy between radio-biological and photo-chemical action is still a 
matter of surprise, even though we are told by modern researchers 
that in many cases the action of light rests on the liberation of 
electrons. 
These phenomena might be correlated by assuming that the 
charged particles which send the radio-active radiation with great 
velocity through the lipoid films on the surface of the cells, evoke’ 
inside the cells a catalytic effect, which we usually call a stimulus *). 
1) On physiological radio-activity. Journal of Physiology. Vol. 53 p. 286. 
55 
Proceedings Royal Acad. Amsterdam. Vol. XXUL. 
