STUDIES IN ARTIFICIAL PARTHENOGENESIS. 245 



were allowed to stand until they became highly susceptible to 

 mercuric chloride and were then treated with a solution of the 

 sublimate in sea-water which contained a trace of hydrochloric 

 acid, they did not lift off membranes. If now the solution of 

 mercuric chloride in acidified sea-water was shaken vigorously 

 for a few minutes it again became potent as a stimulant to 

 membrane elevation. In one experiment 4 cc. of n/io HCl was 

 added to 200 cc. of sea-water. To this was added n cc. of 

 m/iooo HgClo. The resultant solution had a p H below 6.8 and 

 caused no membrane elevation. It was shaken until the p H 

 rose to above 7, but it still remained ineffective. It was then 

 shaken vigorously for several minutes, and the p H rose well 

 above 7. After such shaking it produced membrane elevation 

 generally. The effect of the shaking is to remove carbon dioxide 

 from the solution. It seems certain from this experiment that 

 the presence of carbon dioxide interferes with the production of 

 membrane elevation by mercuric chloride. 



Our first point then is the fact that mercuric chloride causes 

 membrane elevation only in the absence of any considerable 

 quantity of carbon dioxide. 



A second point, which was not investigated as closely as it 

 might have been, is the fact that sublimate treated eggs, if 

 centrifuged one or two minutes after the exposure begins, do not 

 lift off membranes. In one experiment no membranes were 

 lifted off when eggs were centrifuged either one or two minutes 

 after they had been placed in a w/io,ooo HgCl 2 solution. Those 

 centrifuged 3? minutes after being placed in the solution showed 

 membrane elevation in 91 out of 100 cases. The centrifugal 

 force used was 4,968 times gravity and in this experiment the 

 eggs were centrifuged for 40 seconds in each instance. Appar- 

 ently it is not necessary to centrifuge the eggs for as long a time 

 as 40 seconds. In other experiments it was found that centrifugal 

 treatment for only 5 seconds was enough to prevent all but a 

 small percentage of the eggs from undergoing membrane eleva- 

 tion. The reason for the effect of the centrifuge is not certain. 

 A plausible hypothesis, but by no means the only one, is that the 

 mercuric chloride reacts with the jelly of the egg to form mer- 

 curous chloride and chlorine, and that it is the chlorine which is 



