456 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



The action of oocytin upon the sea-urchin egg differs from that of 

 isotonic mammalian blood serum in two respects; firstly in the fact 

 that prolonged exposure of the eggs to oocytin solutions causes cytoly- 

 sis and secondly in the fact that it is potent at a great number of differ- 

 ent dilutions whereas the potency of isotonic serum to induce mem- 

 brane-formation disappears upon dilution of the serum to one-half, or 

 at all events one-fourth, by the addition of sea-water. This differ- 

 ence in behavior is apparent, however, and not real. It is due to the 

 inhibiting action of the proteins which are also present in the serum. 



If isotonic blood-serum be diluted by successive additions of sea- 

 water the membrane-forming power is at first weakened and then 

 disappears, but upon further dilution it reappears and then is retained 

 to very high dilutions. The following are illustrative experiments: 



OX-SERUM SAMPLE III. 

 Eggs sensitized by four minutes' immersion in f m. SrCl 2 



Dilution of the Per cent, of membrane Per cent, of membrane 



isotonic formed in fifteen formed in fifty 



serum. minutes. minutes. 



1 100 100 



1/2 5 50 



1/4 



1/8 . ' Not observed 44 



1/16 100 



OX-SERUM SAMPLE V. 

 Eggs sensitized by four minutes' immersion in f m. SrCl 2 . 



Dilution of the Per cent, of membrane Per cent, of membrane 



isotonic formed in fifteen formed in ninety 



serum. minutes. minutes. 



1 68 100 (none cytolyzed) 



1/2 80 86 (none cytolyzed) 



1/4 (none cytolyzed) 



1/8 16 ( 1 per cent, cytolyzed) 



1/16 1 72 (10 per cent, cytolyzed) 



It is evident that when the membrane-forming power is regained in 

 the higher dilutions the power of inducing cytolysis is also acquired, 

 so that the action of the blood-serum now resembles that of saponin 

 or oocytin in every respect. The failure of cytolysis to appear in 

 undiluted serum is due to the inhibiting effect of the high concentration 

 of Protein which it contains, and even membrane-formation may be 

 inhibited if the concentration of serum-proteins is too high or if addi- 

 tional protein be dissolved in the serum. Such sera will nevertheless 

 induce membrane-formation and cytolysis if they are diluted, the inhib- 

 iting effect of the proteins becoming negligible at a dilution of one in 

 sixteen or one in thirty-two. 



Even membrane-formation by Butyric Acid or by spermatozoa may 



