NATURE OF AGENTS WHICH FORM MEMBRANES 455 



stirring, to each liter of serum. This mixture is kept in a cool place 

 for forty-eight hours, when the supernatant fluid can be decanted. The 

 residue is washed several times with large volmes of 2 per cent, barium 

 chloride solution to remove all traces of serum. The precipitate is now 

 stirred up with tenth-normal hydrochloric acid, warmed to 45 C. 

 using 50 c.c. for the precipitate from each liter of serum. After stirring 

 for an hour or more the mixture is centrifuged and to the clear fluid 

 thus obtained an equal volume of tenth-normal sulphuric acid is 

 added. This solution is allowed to stand at 40 C. for twenty-four hours 

 and then thoroughly centrifuged to remove barium sulphate. To the 

 clear fluid are added four or five volumes of acetone and the mixture 

 is cooled for eight hours or more, at the end of which time the white 

 flocculent precipitate has settled. It can then be collected on a hard- 

 ened filter, washed with ether and dried over sulphuric acid. This 

 preparation, which has been designated Oocytin has been carefully 

 examined by G. W. Clark, who finds that successive samples differ in 

 elementary composition, showing clearly that it is a mixture of two or 

 more substances. It gives all the protein reactions but also yields on 

 hydrolysis notable quantities of Hypoxanthine and a Pentose, but only 

 a trace of phosphoric acid. These products correspond to those which 

 would be yielded by the Nucleosides or glucosidal fractions derivable 

 from the nucleic acids by partial hydrolysis. The presence of appre- 

 ciable amounts of this glucoside in the preparation is of peculiar 

 significance when the glucosidal structure of the Saponins, which are 

 similarly potent in inducing membrane-formation, is borne in mind. 



The membrane-forming power of oocytin acting upon eggs sensi- 

 tized by strontium chloride is very great, comparable in fact with that 

 of the saponins. It will induce membrane-formation at a dilution of 

 one in five hundred thousand. The sensitizing effect of strontium is 

 clearly seen to lie in the fact that it precipitates the oocytin and so 

 concentrates it within or upon the surface of the egg. In concentrated 

 solutions eggs which have been freshly transferred from strontium 

 chloride solution collect a dense precipitate at their periphery which 

 may often mechanically prevent or delay the formation of the fertili- 

 zation-membrane. That the activity of the preparation is not due to 

 contamination by barium or other inorganic substances is shown by the 

 fact that it is inactivated by heating for a few minutes to 80 Q. ; the 

 temperature at which the activity of blood-serum itself is destroyed. 



From the spermatozoa of the sea-urchin, cytolyzed by distilled water, 

 a similar fraction may be prepared having analogous potency in 

 inducing membrane-formation in eggs which have been sensitized by 

 immersion in strontium chloride solution. This material has also been 

 found by Clark to yield notable amounts of a purine base and a pen- 

 tose on hydrolysis. It would appear very probable therefore that 

 membrane-formation in natural fertilization is brought about by the 

 introduction into the egg, within the body of the spermatozoon, of a 

 glucosidal cytolytic agent, which is related to the nucleosides. 



