I'm sioi <><; ICAL EFFECTS OF LACK OF <>\^;EN 1<>.~) 



than that furnished l>v ilu 1 assumption that the oxvgen 

 "stimulates" the heart. 



1 was especially interested iu comparing the elVeHs of 

 lark of oxygen on the boat of the heart in Ctenolabrus and 

 Finnlulus embryos. Does the same difference in behavior 

 toward lark of oxygen exist here as in regard to cleavage? 



The heart begins to beat and the circulation is estab- 

 lished in Ctenolabrus embryos as early as forty-eight hours 

 after fertilization. If such forty-eight-hour-old embryos, 

 which are still contained within the eggs, are introduced into a 

 gas-chamber through which a current of hydrogen is passed, 

 the heart usually comes to a standstill /// from three to fen 

 minutes after the current of </</$ y'.s Inrned on. The activity 

 of the heart does not, however, gradually fall to zero, but the 

 heart comes to a standstill suddenly when the number of 

 heart-beats has decreased but little or not at all. In one case 

 the heart beat about DO times a minute before the hydrogen 

 was admitted. Hydrogen was then passed through the 

 gas-chamber, and after four minutes the heart still beat 89 

 times; two minutes later it beat 78 times, and in the following 

 minute 77 ; in the next minute the heart came to a sudden 

 standstill. After hydrogen had been passed through the 

 gas-chamber for only seven minutes, and when the number 

 of heart-beats had fallen only from 90 to 77 a slight de- 

 crease only --the heart suddenly stood still; at that time 

 blood was still circulating beautifully. 



In a second experiment the number of the heart-beats 

 was 10S per minute at the beginning of the experiment. 

 Two minutes after turning on the hydrogen gas the heart 

 beat 10. "3 times, and three minutes later 1<>S times a minute. 

 During the next minute the heart stood still after having 

 beaten l2:> times in the tirst eighteen seconds of that minute. 

 The heart stood absolutely still for four minutes, after which 

 it gave a few weak pulsations. For the next three minutes 



