404 STUDIES IN GENERAL PHYSIOLOGY 
the Ctenolabrus, and eggs’ which cannot cleave without 
oxygen, the surface layer of the cleavage-cells is liquefied 
and the cells fuse together. The latter fact seems to indi- 
cate that cleavage does not occur in certain eggs, because 
without oxygen profound molecular changes occur, which, 
among other things, prevent the formation of a membrane 
or a specific surface film. 
X. ON THE EFFECT OF LACK OF OXYGEN ON CARDIAC 
ACTIVITY IN FISH EMBRYOS 
The older experiments on the effect of lack of oxygen on 
the activity of the heart have in part led to strange results. 
Tiedemann, for éxample, found that when the heart of frogs 
or salamanders is excised and kept under the bell of an 
air-pump, it ceased to beat in less than one minute when the 
air is rarified.’ Castell’ came to more probable results. He 
found that when the heart is cut out of the body of a frog 
and kept in an indifferent medium in the absence of oxygen, 
it may continue to beat for an hour. In the experiments of 
Pfliger and Aubert, which have already been mentioned, the 
heart continued to beat after all the spontaneous movements 
of the animal had long ceased. 
The older authors had discussed the question as to whether 
oxygen does not have a direct stimulating effect upon the 
heart. This would, of course, explain why the heart ceases 
to beat when oxygen is lacking. Castell, however, showed 
that a heart which has ceased to beat in an atmosphere free 
from oxygen will also not beat when stimulated by other 
means. The papers which have been cited in the introduc- 
tion give a more rational explanation of the role of oxygen 
1 This phenomenon is less distinct, and therefore not so certain, in the egg of Arba- 
cia as in that of Ctenolabrus. Driesch questions it in the sea-urchin egg, but I am not 
certain that his experiments are identical with mine. [1903] 
2 Archiv fiir Anatomie und Physiologie, 1847, p. 490. 
3 [bid., 1854, p. 226. 
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