FERTILIZATION REACTION IN ARBACIA PUNCTULATA. 257 



the use of distilled water in the solutions, and in consequence, 

 the dissociation of the salts could be accurately measured and 

 precipitation did not trouble the investigators. In the work 

 with Arbacia, on the other hand, it was necessary to use sea- 

 water for all of the final solutions though the stock solutions 

 were made in distilled water. The composition of the sea-water 

 is of such a nature that in many cases there is a precipitation 

 and in no case could the ionization of the salt be accurately 

 determined. The sea-water, as it comes from the tap in the 

 laboratory, has a p.H. of 8.0 and I may say here, that in no case 

 did the concentration of the metallic salt necessary to inhibit 

 membrane formation have a p.H. below 7.0. In some of the 

 solutions there was a visible precipitate, as was most evident in 

 the cases of Zinc, Lanthanum, and Lead. In such solutions, 

 the balance of the salts must be disturbed. Thus, in the case of 

 the alkaline earth metals, and silver, tin, manganese, chromium, 

 and iron, the precipitate was so heavy that after a few preliminary 

 experiments, their use was abandoned. The precipitation of 

 zinc, lanthanum, and lead was not great enough to hide the 

 effect of the salts on the elevation of the membranes but when 

 the concentration was increased for the investigation of cleavage- 

 toxicity, the precipitation was so heavy that it was deemed 

 unwise to try to determine that point for them. 



When the series was completed, it was found that the work 

 included tests made with the following metals: Gold, copper, 

 zinc, lanthanum, aluminum, platinum, lead, nickel, cadmium, 

 cobalt, and mercury. The results of the experiments show a 

 similar behav or of the metals, save mercury, and those described 

 by Lillie ('21) for the chloride of copper. The inhibiting concen- 

 tration varies for the different metals. 



The behavior of mercuric salts is peculiar and unexplainable 

 at present. Its solutions seem to favor membrane elevation up 

 to a concentration at which the sperm are immediately paralyzed , 

 while at a much greater dilution, cleavage is completely inhibited. 

 This will be treated in more detail in the following pages. 



Rhubidium and cesium were found to be indifferent up to the 

 isotonic concentration and will not be treated further. 



