278 ANIMAL AGGREGATIONS 



containers with these substances in order to change the survival 

 time. Drzewina and Bohn suggest that in such cases we are deaHng 

 with an electrical phenomenon which they designate as "catalysis 

 by contact." They suggest that animal groups or masses of sperma- 

 tozoa, by the mere fact of their presence in numbers in a limited 

 space, influence each other, causing the individuals to become more 

 or less sensitive, just as they are activated or disactivated above 

 paraffin or stearin; somewhat as inorganic chemicals are more or less 

 sensitive according as they are placed over paraffin or stearin. 



From an entirely different approach Gray (191 5) had suggested 

 that at least a part of the phenomena connected with the physiology 

 of spermatozoa is electrical in nature. We have stated above that 

 the spermatozoa of sea urchins become quiet in acid of proper 

 concentrations and are again activated by making this sufficiently 

 alkaline. He thinks that the movements of the spermatozoa are 

 dependent upon the electrical properties of the cell and of the sur- 

 rounding medium, and cites two lines of supporting evidence. 



If sperm are suspended in a neutral isotonic cane-sugar solution, 

 their activity ceases, but is recovered if a trace of alkali is added. 

 If an electric current of appropriate strength is passed through the 

 neutral solution just mentioned, the sperm tend to collect rapidly 

 about the positive pole. Those remaining around the negative pole 

 become very active. This activity is probably associated with the 

 fact that the region becomes definitely alkaline. If the neutral solu- 

 tion is made slightly acid, neither the migration to the positive pole 

 nor the activation about the negative one takes place. In such a 

 solution the action of the electric current causes the spermatozoa 

 to collect in a well-scattered netlike aggregation. The activity 

 shown can readily be interpreted on the assumption that the active 

 spermatozoa carry a negative surface charge which is lost when free 

 hydrogen ions are present. 



Further (Gray, 1920), if a drop or two of a dilute solution of cerous 

 chloride is added to a weak suspension of Arbacia sperm, the sperm 

 become highly active and aggregate rapidly. The aggregated sperm 

 remain active for some time and then become motionless. These re- 

 sults are attributed to the action of the trivalent cations present. 



