310 STUDIES IN GENERAL PHYSIOLOGY 
opment of the embryo. The details are given in the fol- 
lowing pages. 
I. THE RELATIVE SENSITIVENESS OF THE EMBRYO TO LACK 
OF OXYGEN 
1. The fact that embryonal development soon stops, and 
that the embryo dies without oxygen, has been shown to be 
true so often by experiment that it is not necessary to discuss 
it here.’ I tried to determine, first of all, how long and how 
far development could go in various stages of development 
at the same degree of lack of oxygen; and, secondly, how 
long the embryo could remain exposed to the same degree of 
lack of oxygen in different stages of development without 
losing its power of development. The stages of development 
which were studied were the following: (1) the freshly fer- 
tilized egg; (2) the egg after the formation of the blasto- 
derm, but before the formation of the embryo, about twenty- 
four hours after fertilization; (3) the egg after the beginning 
of the formation of the embryo, about forty-eight hours 
after fertilization (the embryo usually had at this time optic 
vesicles in which the lens was just being formed); (4) the 
embryo just after the circulation was established, seventy- 
two hours after fertilization; and finally various later stages. 
The egg of Fundulus is especially well adapted to these ex- 
periments, because it is very tough, develops fully in the 
aquarium, and the fish hatches in the aquarium. The 
entire period of development takes in summer, at a tempera- 
ture of about 24° C., about twelve to fourteen days. 
The method used in these experiments was similar to that 
of Bunge in his well-known experiments on the need of 
oxygen in lower animals.’ About 6 ¢.c. of potassium hy- 
droxide and pyrogallol are put into a test-tube (according to 
Hempel’s directions). Into this test-tube is introduced a 
1 For the literature on this subject see DUsInG, Pfliigers Archiv, Vol. XXXIIL 
2BuNGE, Zeitschrift fiir physiologische Chemie, Vol. XIV, p. 322. 
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