572 STUDIES IN GENERAL PHYSIOLOGY 
would accelerate the disproportion between the Na and Ca 
ions of the protoplasm. I tried 12 Na,SO, solution. In 
no experiment was a single embryo formed, and in each case 
the development of the germ stopped in an earlier stage 
than in the pure NaCl solution. This corroborates our 
view that the poisonous character of the pure NaCl solution 
is due to the fact that for the development of the egg the Na, 
Ca, and K ions must exist in definite proportions in the 
protoplasm. 
Ina pure 1,?n MgCl, solution no egg candevelop. Even 
in equal parts of 19 MgCl, and distilled water only a small 
proportion of eggs (20 per cent.) were able to form embryos, 
none of which hatched. Mg ions behave toward the egg of 
Fundulus very much like Ca and unlike K ions. In a solu- 
tion of 98 c.c. $n NaCl-+ 2 c.c.1,?n MgCl, all the eggs form 
embryos, although no fish hatch. But in larger quantities 
the Mg ions are not so poisonous as the Caions. Even ina 
mixture of equal parts of $n NaCl+ 1,2» MgCl, as many as 
75 per cent. of the eggs form embryos (although none of 
the latter hatch). This behavior of the Mg ions is similar to 
the one described in my paper on the absorption of liquids. 
The above-mentioned experiments on the effects of K ions 
show very clearly that the effect of these ions upon cell- 
division is altogether different from their effect upon the 
rhythmical contractions. This is not only true for the cells 
of Fundulus, but also for the egg-cells of the sea-urchin. I 
intend to discuss the effect of ions upon the cell-division in 
the eggs of sea-urchins in the next paper. 
Ill. SOME GENERAL CONCLUSIONS 
1. The results of this paper bear upon several other 
problems which we have thus far had no chance to discuss 
sufficiently. There has been a controversy as to whether 
the contractions of the heart are myogenic or neurogenic. 
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