570 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 muscle. 
Ca ions are in small quantities more beneficial, in larger 
quantities more injurious, than Na ions. The addition of a 
little 1,2 CaCl, to a pure NaCl or a pure KCl solution 
causes all the eggs to develop, but very soon a limit in the 
addition of CaCl, is reached where no more embryos are 
able to form. The following table shows this in a very 
marked way: 
TABLE II 
Percentage 
Character of Solution of Eggs That 
Formed Embryos 
100 c.c. §n KC1+ Occ. 19 2 CaCl, 15% 
98 e + 2 a 100 
95 “ ah & “ 100 
90 i +10 “ 100 
75 ef + 25 se 100 
60 se + 40 * 9 
50 " + 50 . 0 
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. Asa rule in a mixture of 75 c.c. n NaCl+ 
25 c.c. 1,91 CaCl, no embryo is formed. 
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