153 



of the three fundamental manifestations, i.e. tonus, excitability and 

 automaticity persist freely, two sorts of automaticity can be elicited 

 by superadding successively the several radioactive elements to 

 the nutrient liquid which surrounds the cells. Two sorts we say, 

 because there are two groups of radio-active elements, which thus 

 far I have been able to use as medium in the solutions of Ringer 

 or Tyrode to substitute vice versa: l^K an «-group: uranium, 

 radium, emanation, polonium, thorium, 2"*^ a /?-group: potassium, 

 rubidium. 



We shall now discuss the points of distinction and of agreement 

 between these alpha-, and beta-automaticities. 



The principal feature of an automatic, periodic movement is its 

 tempo, which in its turn depends again on the so-called refractory 

 stage inserted into every period. Now this tempo is determined by 

 the amount of radio-activity for the alpha-group, as well as for the 

 beta-group. A minimum amount is required for the movements to 

 reveal themselves at all, and a maximum quantum that should on 

 no account be surpassed. This allows a certain latitute for dosages, 

 which is narrow for the alpha-, and broad for the beta-group. 



Somewhere in this latitude there is a point of greatest frequency, 

 the optimum. This point being established for the two sorts of rayers, 

 the frequencies will be the same for either group. 



Such an investigation evidently requires a constant temperature. 

 It is also clear that, when the temperature is variable the two 

 determining factors: amount of radio-active matter and degree of 

 the temperature, may cooperate or counteract each other. It has 

 already been shown that there is a law, which determines these 

 relations, but I do not intend to enter into it here. Now, when both 

 for potassium and for uranium the optimum doses have been found, 

 which yield the highest frequency, the frequencies for potassium- 

 and for uranium-automaticity are equal. This is instanced in Fig. J . 

 In the centre the potassium-beat is shown, separated to the right 

 and to the left by a standstill from two other pulsations; these two 

 other pulsations represent the paradoxical phenomenon appearing 

 when passing from perfect potassium-dosis to a perfect uranium- 

 dosis, and conversely ^). To the right and to the left the uranium- 

 beat can be observed. Its frequency does not ditfer from that of the 

 automaticity in the centre of the figure. 



Another property the two automaticities have in common is a 



1) These Proceedings Vol. XIX, p. 1043, (1917) G. R. Soc. de Biol. t. 84 p. 704. 

 Paris 1921. 



10* 



