577 



fusing the lieart alternately willi Ringer-soliitions of vaiions com- 

 position. First we determined tlie minimum dosis of potassinm- 

 chloride tiiat the individual lieart required, after which it was per- 

 fused with a RiNGiiK-solution, wiliiout potassium until it came to a, 

 standstill. After ten minutes, in which interval we ascertained tliat 

 no latent automaticity existed, we proceeded to caesium perfusion. 

 We determined in succession the minimum-, the optimum- and the 

 maximum-doses. The dosage was gradually increased with the great- 

 est care. By means of an air-injector, such as was used by Locke 

 and Rosenheim, the same 7i or 1 Liter of circulating fluid was sent 

 round. The fluid that went through the heart was thus loaded with 

 as much oxygen as is soluble in a weak salt-solution. 



The dosis of potassium-chloride and of caesium-chloride that proved 

 just sufficient to make the heart beat regular!}', was considered as 

 the minimum dosis; as optimum dosis we took the one which yielded 

 the greatest frequency and maintained it. It was difficult to find the 

 maximum-dosis, because an increase in the caesium dosage brings 

 on an inconvenient negative inotropism. 



We then considered as highest practicable dosis the one which 

 produced lytic symptoms of cessation of contractility. Strictly the 

 maximum dosis lies somewhat higher. Meanwhile tiie caesium has 

 penetrated deep into the heart-cells, for it takes hours bel'ore a heart 

 can be deprived of the profusion of caesium and before its action 

 can be arrested by a RiNGEH-solution that contains neither potassium 

 nor caesium. 



A survey of our results can again be best obtained by an inter- 

 comparison of caesium and potassium. 



Minimum-dosis of the impure preparations. 



The minimum-, optimum-, and highest practicable doses are, for 

 the impure preparations in milligrammes of caesium-chloride [)er Liter 

 on an average in the ratios of: 



1194 : 1538 : 1Ö9&. 



min. opt. highest pract. 



38 

 Proceedings Royal Acad. Amsterdam. Vol. XXVI. 



