PH YsioMH! I(\\L KITKCTS OF LACK OF OXYGEN 375' 



supported liv the fact that Hit- eggs of Fundulus in which 

 such structural changes do not occur in the alisence of 

 oxvgen even after twenty-four or more hours, continue to seg- 

 ment for more than twelve hours in the absence of oxygen. 



What we are going to show for cleavage holds also for 

 other life-phenomena, for example, the activity of the heart. 

 We find that the heart of the Ctenolabrus embryo comes to 

 a standstill so quickly after the oxgen has been withdrawn 

 that it is impossible to think that the source of the energy 

 for the beating of the heart has given out, while the heart 

 of the Fundulus embryo continues to beat for many hours 

 under similar conditions. It is possible that in this case 

 also structural changes occur which are similar to those 

 which we are able to observe directly in the cleavage-cells. 

 These changes render impossible the transformation of 

 chemical energy into mechanical energy in the contraction 

 of the heart of the Ctenolabrus embryo. 



Such molecular changes as manifest themselves by struc- 

 tural changes can be brought about just as well through 

 processes of reduction due to the lack of oxygen as through 

 the injurious compounds which may be formed in the absence 

 of oxygen. 



The facts which we obtained by the biological study of 

 the effects of lack of oxygen may also again be of importance 

 to the physiological chemist. We shall meet with some 

 facts in this paper which will serve to illustrate the view of 

 Bunge that in all probability the greater part of the energy 

 necessary for considerable work of the muscles is furnished 

 through processes of oxidation (and not through processes of 

 hydrolvsis). The frequency of the heart-beat of the Fundu- 

 lus embryo decreases steadily during the period during 

 which oxygen is withdrawn, until it reaches the minimum (of 

 about t \\vntv beats per minute), when all the oxygen has dis- 

 appeared. But the In-art can In-at for ten hours at this rate 



