S.PERM FILTRATES AND DIALYZATES. 



Godlewski (1911); Herlant (1912); Heilbrun (1915); and Lillie 



(1911, 1915. 1921)- 



What real evidence have we to support the suggestion, re- 

 current in one form or another, that the sperm exude a substance 

 which facilitates fertilization ? The early attempts of Spallanzani 

 (loc. '/.), with nitrates, and of Prevost and Dumas (loc. cit.), 

 with nitrates and extracts of spermatozoa, to demonstrate such 

 a substance gave purely negative results. In later work: Pierri 

 (1899); Winkler (1900); Du Bois (1900); Gies (1901); Pizon 

 (1905); Jacoby (1910); Morse (1912); Robertson (1912); Foa 

 (1918) positive results, where reported, are actually vitiated by 

 errors of technique or interpretation, Loeb (1913. P- IO4> and 

 1916, p. 203); and Lillie (1919. PP- 133. 134)- 



II. METHODS. 



In an investigation of this kind so much depends upon the 

 methods employed that it seems desirable to present these in 

 some detail. 



All glassware was cleaned with potassium-bichromate-sulphuric 

 acid mixture, subsequently removed by washing in fresh and in 

 sea-water. All solutions were made with analyzed chemicals 

 (Kahlbaum's, Merck's, and Baker's) with water redistilled from 

 glass. Specific gravity was determined in early experiments 

 with a standard hydrometer and later with a Westphal balance. 

 A special set of indicators and standards provided and tested at 

 intervals by Hynson, Westcott and Dunning was used for the 

 colorimetric determination of the hydrogen-ion concentration, 

 Clowes and Smith (1923 and 1924). Every possible precaution 

 was taken to avoid accidental insemination and sea-water controls 

 accompanied every experiment. 



Method of Obtaining Ripe Reproductive Cells of Sea-urchins. 

 One method is as follows: The instruments and hands of the 

 operator are thoroughly washed in tap water and the animals 

 are washed in tap water followed by sea-water. They are opened 

 by cutting through the oral disc with sterile scissors, the disc 

 and the alimentary canal are removed with sterile forceps and 

 the coelom is flushed with filtered sea-water to remove the body 

 fluids and any intestinal contents. Males and females are 



