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.’”! 
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 HCl, exactly 
neutralizing the extract with Ba(OH)., redissolving the precipi- 
tate in N/10 H,SO, 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. 
Robertson also found that Witte’s peptone contains a mem- 
brane-forming substance demonstrable by eggs previously 
treated with SrCl,. He thinks it unlikely that the active sub- 
stance is a lipoid.? 
1 Robertson, Archiv f. Entwicklungsmechanik, XXXV, 70, 1912. 
2 Robertson, Proc. Society for Exper. Biol. and Med., X, 117, 1913. 
