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The Electrical Conductivity of Fertilized and 

 Unfertilized Eggs. 



By 



J. Gray, B.A., 



King's College, Cambridge. 



The following is a preliminary account of some experiments carried out 

 this summer at Plymouth, They were undertaken with a view to the 

 investigation of the changes, both physical and chemical, which are 

 induced in the egg by the entrance of a spermatozoon. 



No attempt is made to discuss the results in the light of current theories 

 regarding the phenomena of fertilization, as it is hoped that further 

 work will make such discussions more profitable than would be the case 

 at present. 



Apparatus. 



In order to determine the electrical conductivity of the eggs, a con- 

 ductivity cell was used such as would fit the holder of a small hand 

 centrifuge. The tube was about 10 cm. long and 1 cm. in diameter. 

 The electrodes were two sc^uare platinum plates each possessing two equal 

 surfaces of 25 sq. mm. These were fixed about 25 mm. apart and were 

 carried by two silver wires which passed through glass tubes, and which 

 were fixed through the stopper of the tube. 



In some of the earlier experiments the volume of the eggs in the tube 

 was determined by marking their level with a fine pointed grease pencil,, 

 but in all the later experiments the tube was graduated. 



This form of conductivity cell has two advantages — it fits into the 

 holder of an ordinary centrifuge, and the volume of eggs required is small. 

 The latter point is of great importance, quite apart from, the difficulty in 

 obtaining large quantities of ripe Echinus eggs. If too many eggs are 

 enclosed within a tube, it is not only impossible to ensure a good per- 

 centage of fertilizations by adding a small quantity of sperm, but the over- 

 crowding of the eggs interferes very considerably with the development 

 of the eggs subsequent to fertilization, i.e. the rate of division differs very 

 considerably from that of similar eggs in a large bulk of water ; in extreme 



