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STUDIES IN GENERAL PHYSIOLOGY 



As soon, however, as the heart begins to beat and circu- 

 lation becomes necessary for the embryo, the K ions become 

 more poisonous than the Na ions. Only in the first three 

 solutions is the heart of the embryo able to beat for a few 

 days. But even in these solutions no embryo lives longer 

 than about a week. In the other solutions the embryos die 

 much earlier. This should certainly serve us as a caution in 

 taking it for granted that the cell-division is due to con- 

 tractile phenomena of the same order as those occurring in 

 the niuscle. 



Ca ions are in small quantities more beneficial, in larger 

 quantities more injurious, than Na ions. The addition of a 

 little y n CaCl 3 to a pure NaCl or a pure KC1 solution 

 causes all the eggs to develop, but very soon a limit in the 

 addition of CaCl 2 is reached where no more embryos are 

 able to form. The following table shows this in a very 

 marked way: 



TABLE II 



In none of these solutions was an embryo able to hatch or 

 to live through the whole period necessary for develop- 

 ment. The K ions in these solutions caused a cessation of 

 the heart-beat. The more K ions the solution contained, 

 the sooner this happened. In mixtures of Na and Ca ions 

 the limit where Ca ions prevent the formation of an embryo 

 is still lower. As a rule in a mixture of 75 c.c. -f- n NaCl + 

 25 c.c. *-gn CaCl 2 no embryo is formed. 



