STUDIES OF FERTILIZATION. 



VII. Analysis of Variations in the Fertilizing Power of 

 Sperm Suspensions of Arbacia. 



FRANK R. LILLIE. 



I. Introduction 229 



II. Experiments 231 



1. Methods 231 



2. The Optimum Curve of Dilutions 233 



3. Curves of Successive Half -Dilutions 235 



4. Time as a Factor in the Fertilizing Power of Sperm Suspensions of 



Different Concentrations 239 



5. Other Factors in the Fertilizing Power of Sperm, Suspensions 244 



III. Discussion 246 



I. Introduction. 



In his epoch-making "Experiences pour servir a I'histoire de 

 la generation des animaux et des plantes" published in 1785 the 

 Abbe Spallanzani describes among his numerous experiments on 

 fertilization and artificial parthenogenesis some determinations 

 concerning the minimal quantity of sperm necessary to fertilize 

 the eggs of the frog. He found that be could get perfect fertili- 

 zation with seminal fluid diluted 2,720 times with water. At 

 greater dilutions the percentage of fertilized eggs began to fall 

 off, but some eggs fertilized up to a dilution of about 20,000 

 times. He calculated that the weight of the "spermatic par- 

 ticles" necessary to fertilize an egg was 1/2,994,687,500 of a grain, 

 and that the volume of the egg in proportion to the volume of 

 spermatic particles necessary to fertilize it is as 1,064,777,777: i. 

 In 1824 Prevost et Dumas confirmed these calculations. 



So far as I know such experiments have not been repeated. 

 The reason for this would appear to be that when it was once 

 established that only a single spermatozoon unites with each 

 ovum in fertilization all such quantitative studies of the fertilizing 

 power of sperm dilutions appeared to have lost their point. So 

 long as it was assumed (as was generally the case) that the fertiliz- 

 ing power of the spermatozoon is a function of its motility 



229 



