296 STUDIES IN GENERAL PHYSIOLOGY 
be called a specific cardiac poison only in so far as the heart 
ean be brought to a standstill with a much smaller dose than 
is required to poison the remaining organs of the embryo. 
2. At a temperature of 20° C., and with a plentiful sup- 
ply of oxygen, the embryos of Fundulus develop in about 
twelve to fourteen days in normal sea-water. Under these 
conditions the heart begins to beat about sixty to seventy 
hours after fertilization. If Fundulus embryos four to six 
days old are placed in sea-water to which 1.5 g. of KCl have 
been added to each 100 c.c. of sea-water, the heart ceases to 
beat, and death ensues in about one hour, at the outside, 
in all the embryos. That the poisonous effect of the potas- 
sium is not limited to the heart is shown by the fact that the 
embryo becomes exceedingly restless before the heart ceases 
to beat. An entirely different series of phenomena ensues 
when the Fundulus eggs are introduced into the same salt 
solution about one-half hour after fertilization. The eggs 
develop in an entirely normal way, the embryos live until 
the fifth or sixth day, and the cramp-like movements do not 
set in. Furthermore, I noticed in a few of these embryos 
very weak and very slow pulsations of the sinus venosus on 
the third or fourth day. 
This activity of the heart did not, however, appear in all 
the embryos, and when it did appear it did not last long. 
In no case, however, was the beat of the heart sufficient to 
cause a circulation of the blood. The circulation in the 
yolk-sac of the Fundulus embryo can be demonstrated more 
clearly and easily than the circulation in any of the ordinary 
preparations used for this purpose. 
In the normal embryo the circulation is very marked, even 
some seventy-five hours after fertilization; but it does not 
matter how long one waits in the case of the embryos poisoned 
by adding 1.5 g. of KCl to each 100 c.c. of sea-water—never 
did I succeed in discovering even the slightest indication of 
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