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. OX 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 example, 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. 2 Castell 3 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 

 Pfliiger 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 Af ba- 

 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. [1903J 



2 Archiv fur Anatomic und Physiologic, 1847, p. 490. 



3 Ibid., 1854, p. 226. 



