200 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



mortar, filtered, and the filtrate tested for its action. This 

 filtrate is exceptionally active. 



Robertson described a more complicated process of precipi- 

 tating the active substance of the blood with acetone, which 

 was based on the assumption "that the fertilizing agent might 

 be precipitable by alkaline earths." 1 



He has since improved this method and gives the follow- 

 ing description: Precipitation from the serum by acetone, 

 extraction of the precipitate with hot N/10 HC1, exactly 

 neutralizing the extract with Ba(OH) 2 , redissolving the precipi- 

 tate in N/10 H 2 S0 4 and reprecipitating it with acetone. The 

 yield from a liter of ox serum lies between 10 and 40 milligrams. 

 From its reactions Robertson concludes that the substance is 

 either a protein or a peptone. One part of the substance rubbed 

 up in 512,000 parts of sea-water caused membrane formation 

 in 80 per cent of the eggs of S. purpuratus which had previously 

 been sensitized by four minutes' immersion in 3/8 m SrCl 2 . 



Robertson also found that Witte's peptone contains a mem- 

 brane-forming substance demonstrable by eggs previously 

 treated with SrCl 2 . He thinks it unlikely that the active sub- 

 stance is a lipoid. 2 



1 Robertson, Archiv f. Entwicklungsmechanik, XXXV, 70, 1912. 



2 Robertson, Proc. Society for Exper. Biol. and Med., X, 117, 1913. 



