ROBERT F. LOEB 235 



development of the eggs of Arbacia cannot be attributed to its very- 

 slight radioactivity. 



These results would seem at variance with the findings of Zwaarde- 

 maker and his coworkers in their experiments on the heart were it 

 not for the fact that they also were able to replace potassium by 

 cesium, which Zwaardemaker designates as "physiologically but not 

 physically" radioactive. As a matter of fact nobody has thus far 

 shown that Cs possesses more radioactivity than any other non- 

 radioactive element; e.g., Na. Zwaardemaker's observation that a 

 heart which has ceased to beat in a solution lacking KCl can be resus- 

 citated by radioactive substances may be explained without the as- 

 sumption that K acts through its radioactivity. Lingle^ found that 

 when the ventricle of the heart of the turtle was suspended in a moist 

 chamber where the air was replaced by pure oxygen the strip was 

 able to beat for a considerable time, as long as 3 days, after the beats 

 had been initiated by submersing the ventricle for a short time in a 

 pureNaCl solution. The beats continued in some cases until the putre- 

 faction of the heart tissues put a stop to them. This experiment 

 proves that the KCl is not needed to provide the stimulus for the 

 heart beat but that it is only needed to counteract some of the toxic 

 effects of a pure NaCl solution when the heart is submersed in such a 

 solution. Lingle found, moreover, that the heart which had stopped 

 beating in a pure solution of NaCl began to beat again when 10 cc. of 

 3 per cent H2O2 were added to 90 per cent of the isotonic solution of 

 NaCl. He could show by control experiments that only the bubbles 

 of O2 with which the muscle became frosted were responsible for the 

 resuscitation. The ventricle thus resuscitated could then continue 

 to beat for many hours, Lingle suggests that the oxygen supply in 

 a solution is inadequate for a heart beating in a pure solution of NaCl 

 unless a more rapid source of supplying oxygen than mere diffusion 

 from the air is provided. We do not know how the increased supply 

 of oxygen can resuscitate the heart which had ceased to beat in a 

 pure solution of NaCl but the tentative suggestion may be permitted 

 that this effect is due to the transformation of a harmful substance 

 formed during the activity of the heart in the absence of K, or Ca, or 



3 Lingle, D. J., Am. J. Physiol, 1902-03-, viii, 75. 



