STUDIES OF FERTILIZATION'. 12*J 



solution is accordingly given as one part in 500,000. This is 

 approximately 1/67,000 N, but on account of the alkalinity of 

 the sea-water the effective concentration must be somewhat less. 



In some early experiments a stock solution of copper sulphate 

 in sea-water was used. The strength of this declined rapidly 

 and it was used only in experiments I to 9. Its physiological 

 effects are the same as copper chloride. 



For each experiment there are two standard controls, viz. : 

 (i) the copper control, i.e., an identical insemination in copper 

 chloride of the same concentration, and (2) gamete control, i.e., 

 an identical insemination in sea-water. Special experiments had 

 in addition their special controls. 



III. EXPERIMENTS. 



i. The Phenomenon of Copper Inhibition. Relations between 

 copper concentration and sperm concentration. 



The presence of one part of copper chloride in 500,000 parts 

 of sea-water will completely inhibit fertilization of the eggs of 

 Arbacia. Previous exposure of the gametes to the action of the 

 copper chloride is not necessary for this result; if eggs and sperm 

 are dropped simultaneously into the copper-containing sea-water, 

 and mixed at once, no reaction occurs, though the sperm are as 

 active as in normal sea-water. With most batches of eggs the 

 inhibition is complete even when the amount of sperm used is 

 several times what is necessary to fertilize 100 per cen j ;. of the 

 eggs in normal sea-water. 



Though the eggs may be bombarded by hundreds of sperma- 

 tozoa each, they do not usually give the first beginnings of the 

 fertilization reaction; but, if any egg does so, fertilization is 

 carried through to completion in the copper solution, and the 

 egg segments. The inhibition is thus an "all or none" effect, 

 as is shown more fully beyond. 



The relations between copper concentration and sperm concen- 

 tration are given in Table I. If the concentration of the copper 

 is much greater than one part of copper chloride in 500,000 

 parts of sea-water, the inhibition may be regarded as complete 

 for all sperm concentrations. 



