296 STUDIES IN GENERAL PHYSIOLOGY 



be called a specific cardiac poison only in so far as the heart 

 can 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 KC1 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 KC1 to each 100 c.c. of sea-water never 

 did I succeed in discovering even the slightest indication of 



