106 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



hypertonic solution remains practically ineffective in the pres- 

 ence of a minute quantity of potassium cyanide, but that the 

 eggs are not in the least injured by the latter in so short a time. 

 It can be directly shown that the hypertonic solution is 

 effective only in the presence of free oxj^gen, by simply expelling 

 the air from the hypertonic solution. But this experiment 

 can very easily miscarry on account of the interference of a 

 troublesome source of error. Usually the hypertonic solution 

 can be freed as far as possible from oxygen by passing through 

 it for several hours a current of scrupulously purified hydrogen. 

 Then a drop or two of eggs are placed in the solution. And 

 herein lies the source of error. On opening the flask, of course 

 some oxygen enters it, and for a short time the hypertonic 

 solution is acting, not in the absence, but in the presence, of 

 some oxygen. Now obviously only a little oxygen is sufficient 

 to maintain the processes of oxidation which underlie the 

 development of the egg. I had already noticed this eighteen 

 years ago in my first experiments upon the necessity of oxygen 

 for normal cleavage. But, as already mentioned, the eggs 

 need to remain only a short time some thirty to fifty minutes 

 in the hypertonic solution after membrane formation, and it 

 is clear that in so short a time the introduction of a little oxygen 

 into the hypertonic solution may easily frustrate the whole 

 experiment. I reduced this risk by opening the stopper of the 

 flask with the aid of a skilled assistant for only about a second 

 and for a distance of only a millimeter in order to introduce 

 the eggs. Before, during, and immediately after the opening a 

 very strong current of hydrogen, was passed through the flask. 

 Negative experiments, i.e., ones in which the hypertonic solu- 

 tion caused a few or many of the eggs to develop, even after 

 the passing of a current of hydrogen, do not prove much; 1 but 



1 They only show that too much oxygen was present inadvertently in the 

 hypertonic solution. I indicated this source of error in my first note upon the 

 subject: Loeb, "On the Necessity of the Presence of Free Oxygen in the Hyper- 

 tonic Sea-Water for the Production of Artificial Parthenogenesis," University of 

 California Publications, Physiology, III, 39, 1906. 



