IMMUNITY AND SUSCEPTIBILITY OF SEA-URCHIN EGGS. 233 



its effect in augmenting the normally occurring increase in the 

 pressure, and the point of greatest susceptibility would be at such 

 points and also at that of the normal maximum pressure, viz., just 

 before or during cleavage. This explanation therefore accords 

 best with the sharp rise in the curve, and is supported also by the 

 evidence from the parthenogenetic methods for Arbada, in which 

 the pressure is first increased, sometime before the cleavage, which 

 takes place after the return from the hypertonic solution to the 

 sea water. 



The characteristics of the above curve were confirmed in general 

 by Experiment IV., B and C, already presented, and more 

 especially by three subsequent experiments, as can be seen from 

 the following records : 



EXPERIMENT V]I. 

 August 22, 1/64 sat. sol. Time of exposure, 1/2 hr. 



Experiments P//7. and IX., August 23 and 29. Solution, 

 one sixty-fourth saturated ether, one half hour exposure. Lot 

 i. one half hour after fertilization all living. Lot 2, during- see- 



o o & 



mentation, all dead in 2-cell stage. 



EXPERIMENTS WITH HC1. 



Preliminary and theoretical. According to the views that we 

 have previously discussed the hydrogen ion in the case of the 

 nerve is held to inhibit the stimulating action of the chlorine ion, 

 "overbalancing' 1 this more than do either K, Li, NH 4 or Na. 

 This may be due to the greater velocity of diffusion of H, which 

 is 325, that of Cl 70.2 at 25 C. 1 On the other hand it has been 

 supposed that the H ion brings about the parthenogenetic devel- 



1 Ostwald. 



