380 H. H. NEWMAN. 



At the suggestion of Dr. A. P. Mathews I took up this prob- 

 lem to see whether the surface tension, or the condition of the 

 surface of the egg was of importance in determining fertilization. 

 The working hypothesis was that the surface of the egg possessed 

 a certain definite tension that rendered it permeable to sperm of 

 equally definite surface tension. If the tension of either the egg 

 or sperm is altered their fusion might no longer be possible, 

 although the sperm of other species that might chance to possess 

 a more appropriate surface tension might enter. 



If the egg be a colloidal system with a membrane of a certain 

 definite surface tension it should be possible so to alter this ten- 

 sion by the use of certain salts, that the sperm of the same species 

 can no longer enter, and after so doing, to reverse the process 

 and restore the original surface tension and the consequent per- 

 meability. 



According to Mathews 1 the surface tension of colloidal particles 

 or particles in suspension may be increased or decreased by 

 means of salts acting through their tension coefficients. The 

 egg may be regarded as a particle in suspension of which the 

 membrane is electro-negative. It should be possible to increase 

 its surface tension by neutralizing these charges either wholly or 

 in part. A list of the tension coefficients of salts is given in 

 Mathews' paper on the precipitation of colloids and at his sug- 

 gestion I tried the alkaline earth chlorides, and particularly 

 calcium chloride, as a salt which should increase surface tension, 

 and sodium sulphate as a salt which should have an opposite 

 effect on the surface of the egg. 



The eggs of the minnow, Fundulus heteroclitus, were chosen for 

 the experiment. These eggs are almost immune to changes in 

 the osmotic pressure of the medium. It was noticed at the outset 

 that eggs of F. heteroclitus became incapable of fertilization by 

 their own sperm after exposure to sea water for periods in excess 

 of an hour or in some cases an hour and a quarter. It seemed 

 possible that the cause of this loss of susceptibility to fertilization 

 might be due to certain salts in the sea water. This matter is 



o 



partially cleared up by what follows. 



The first experiments were undertaken to determine which 

 'Mathews, Ameri an Journal of Physiology XIV., 1905, p. 203. 



