STUDIES OF FERTILIZATION. 12 9 



It will be noticed that inhibition is marked even at as low a 

 concentration as one part of copper chloride in 2,500,000 parts 

 of sea-water at a normal sperm concenttation. Most of the 

 experiments to be described were done with 1/500,000 copper 

 chloride, at which concentration no eggs fertilize at normal 

 sperm concentrations. 



If much higher concentrations of sperm are used small per- 

 centages of eggs, varying somewhat in different experiments, 

 may fertilize. (See last items of Table I.) There is thus a 

 certain virtue in mass action of the sperm in the presence of 

 this inhibitor of fertilization; this is somewhat difficult to under- 

 stand, because only one spermatozoon penetrates usually. If 

 we regard the spermatozoa, or some substance borne by them, 

 and the copper as reacting with the same substance of the egg, 

 it can be understood how the sperm substance could replace the 

 copper in some cases when present in excess; or it may be 

 possible that excess of sperm protects the eggs to a certain 

 extent by combining with the copper and thus reducing the 

 amount acting directly on the eggs. 



2. Reversibility of Copper Inhibition. 



Eggs that have been exposed to copper, whether in the presence 

 of sperm or not, may be fertilized after return to sea-water 

 provided that the exposure has not been long enough to injure 

 their vitality too much. In other words, the inhibition by 

 copper is reversible, and the phenomenon is to be regarded as 

 one of inactivation of a substance, not of its destruction. In 

 this respect, the phenomenon is precisely like the inactivation 

 of an enzyme by mercury or copper salts, which is similarly 

 reversible, and which has been shown to be due to a combining 

 of the ions in question with constituents of the enzyme solution 

 (v. Euler and Svanberg, 1920). 



3. Effect of Copper Chloride on Spermatozoa and Eggs Separately. 

 A suspension of spermatozoa in 1/500,000 copper chloride has 



been tested up to 8 minutes exposure of the spermatozoa by 

 fertilizing eggs in sea-water without any noticeable diminution 

 in the fertilizing power of the sperm. The fertilizing power of 

 a sperm suspension made in 1/25,000 copper chloride in sea- 



