712 STUDIES IN GENERAL PHYSIOLOGY 
pressure of which is about equal to that of a $m sodium- 
chloride solution,’ but also in distilled water, or in sea-water 
the concentration of which has been doubled (by the addi- 
tion of NaCl). In the following experiments, therefore, we 
need not at all consider the osmotic pressure of the sur- 
rounding solution. Secondly, since enormous numbers 
of the eggs can be obtained, it is an easy matter to per- 
form the experiments upon hundreds or thousands of eggs 
at once. 
The eggs were artificially fertilized in the laboratory by 
the addition of sperm, and then immediately distributed into 
the various solutions. The embryo forms in from about 
twenty-six to forty-eight hours—varying with the tempera- 
ture —and twenty-four hours later the heart begins to beat, 
and the circulation is established. Usually about two hun- 
dred eggs were put into a solution, and after two or three 
days the developed embryos were counted and the per- 
centage of the eggs which had developed was determined. 
The eggs were kept under observation as long as the 
embryos remained alive. Usually when an embryo was 
once formed, development went farther, and the circulation 
was established. 
2. First of all the toxic effects of a pure sodium-chloride 
solution at various concentrations were tested. Ina NaCl 
solution every egg produced an embryo which died, how- 
ever, before, or immediately after, emerging from the egg. 
(The embryo hatches from between twelve to twenty days 
after fertilization.) On the other hand, in a 3m NaCl solu- 
tion only a few of the eggs gave rise to embryos—about 1 to 
5 per cent. Ina¢m NaCl solution an embryo forms but 
rarely, and in a 3m NaClsolution the formation of embryos 
is rendered impossible. The egg goes through the first 
1m represents that degree of dilution of a solution which contains one gram- 
molecule of the substance in one liter of the solution. 
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