284 ANIMAL AGGREGATIONS 



or fatal concentration for the sperm than in the case of artificial 

 dilutions. 



In Walton's cases, where all dilutions were under controlled arti- 

 ficial conditions, three separate factors, each influenced by quanti- 

 tative considerations, may influence the result, (i) The probability 

 of any one spermatozoon reaching the fertilizable ovum within the 

 time that the ovum is fertilizable is small; and the probability of 

 such success is greater, within limits, the greater the number of 

 sperm introduced. (2) Spermatozoa are variable and are not aU 

 equally capable of fertilizing, so that, again, the probability of fer- 

 tilization is greater, within limits, the greater the number of sperm 

 present. Finally (3), the toxicity of the medium may well act dif- 

 ferentially on sperm suspensions under natural conditions, just as 

 it has been shown to act in laboratory experimentation. This as- 

 sumes that there is a general toxicity to sperm in the female genital 

 tract which would act more vigorously upon the more dilute sperm 

 suspensions. 



In summary, we have found uniform agreement concerning the 

 greater functional longevity of the more dense sperm suspensions, but 

 a not unexpected lack of uniformity in the explanations advanced 

 for this phenomenon. Recapitulating the latter, we find the more 

 rapid exhaustion in dilute suspensions attributed to — 



1. More rapid movement, exhausting sperm energy (Gemmil). 



2. Dilution of nutritive spermatic fluid (Gemmil). 



3. Greater diffusion of substance from spermatozoa necessary for 

 fertilization (F. R. Lillie). 



4. Effect of self-produced CO2 (Cohn). 



5. Decreased production of an autoprotective secretion (Drzewina 

 and Bohn). 



6. Unfavorable electric relations (Drzewina and Bohn). 



7. Allelostasis (Gray). 



Of these, evidence has been produced that throws grave doubt 

 upon the second. Cohn's observation that the total amount of CO2 

 per unit is practically the same, regardless of dilution, is strong 

 negative evidence; and the supporting evidence produced by Gem- 

 mil as a result of treating sea-urchin sperm with nutritive solution 



