386 H. H. NEWMAN. 



ent. It seems probable that the egg and sperm of the same indi- 

 vidual have a slightly incompatible surface tension of egg and 

 sperm, an incompatibility that may be removed by the action 

 of ether. It may also be readily understood why the sperm of 

 one individual is not equally effective on the eggs of all other 

 individuals, for some eggs have a surface tension more suitable to 

 that of the sperm than others. 



If in any way one could overcome the difficulties of surface 

 tension and could inject the sperm of unrelated forms beyond the 

 egg membrane without injuring the egg, we might get some very 

 significant results. This is a field as yet unexplored but I hope 

 not unpromising. These experiments will probably be continued 

 with other eggs and over a more extended field. 



SUMMARY. 



1. The calcium salts are the most active of the salts found in 

 sea water in inhibiting fertilization. They are also the most 

 active salts in precipitating colloids. Hence there is probably a 

 causal relation between the precipitation of colloids and the in- 

 hibition of fertilization. 



2. The seven salts CaCl 2 , Bad,, SrCl 2 , MgCL LiCl, NaCl, and 

 KC1 inhibit fertilization in the order of their tension coefficients. 

 Thus the egg is acted upon as if it were a colloidal system. 



3. Supposing the egg to be a colloidal system with a mem- 

 brane negatively charged it should be possible to precipitate or 

 coagulate this membrane by salts of high positive tension coeffi- 

 cients, such as CaCl.,, and to redissolve this precipitate or coagu- 

 lum by the use of salts of high negative tension coefficients, such 

 as Na.,So 4 . This was done successfully, fertilization being in- 

 hibited by CaCl 2 and restored by Na 2 SO 4 . 



4. This alteration in the character of the membrane must in- 

 volve an alteration in the surface tension that controls the en- 

 trance of the sperm. 



5. The short term of susceptibility of the egg to fertilization 

 by its own sperm, when the eggs are allowed to stand in sea 

 water is probably due to the presence of calcium salts that slowly 

 coagulate the membrane and thus increase its surface tension. 

 The period of susceptibility to fertilization is considerably pro- 



