62 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
nuclear membrane and other nuclear constituents.!. Such a 
liquefaction must of course occur at each nuclear division; 
but I believe that it is only an indirect result of chemical 
processes set up in the egg by the hypertonic solution, and not a 
direct effect of the hypertonic solution. 
Now since the hypertonic solution works entirely in virtue 
of its osmotic pressure, and since the osmotic pressure depends 
only upon the number of molecules or ions in the unit volume 
of the solution, and not upon the chemical nature of the mole- 
cules or ions, all isosmotic solutions should be equally effective 
in causing the unfertilized egg to develop. This is approxi- 
mately true (see also chap. xiii), except that solutions containing 
poisonous salts, e.g., copper salts or others, cannot be used for 
this purpose. 
The closer the hypertonic solution approaches sea-water in 
its composition, the less harmful become the secondary effects 
of the hypertonic solution. For this reason I generally use for 
the preparation of the hypertonic solution sea-water whose 
concentration has been raised to the desired pitch by the addi- 
tion of a suitable amount of a 23 m NaCl, or Ringer, solution. 
The minimal concentration in which different hypertonic solu- 
tions are effective varies somewhat with the different substances 
under consideration. 
2. My next experiments aimed at determining whether the 
results here detailed are only a peculiarity of sea-urchin eggs 
or whether artificial parthenogenesis can be produced in the 
eggs of all animals. In so doing it was at first immaterial to 
me through what method the activation of the egg succeeded, 
so long as it was only possible to cause the unfertilized eggs to 
develop. But the experiments must be briefly mentioned here, 
since the experience obtained thereby had an influence upon the 
further development of this line of research. I had already been 
able to show in the year 1900 that the eggs of a marine worm, 
1 Loeb, Am. Jour. Physiol., IV, 178, 1900. 
