NATURE OF AGENTS WHICH FORM MEMBRANES 457 



be inhibited by the addition of proteins to the sea- water. The following 

 table shows the relative efficiency of various proteins in inhibiting 

 membrane-formation : 



Highest observed Lowest observed 

 concentration which concentration which 

 permits membrane- prevents membrane- 

 formation by formation by 

 Protein. butyric acid. butyric acid. 



Mixed serum proteins 3.7 7.4 



Gelatin .. . . . 1.0 2.0 



"Insoluble" serum-globulin .... 0.3 0.6 



Casein , ... 0.25 0.5 



Ovomucoid. . ... . . . . . 0.125 0.25 



It is a very striking fact that the order of effectiveness of these 

 proteins in preventing the formation, of membranes is the reverse 

 order of their ability to pass through a porcelain filter. It has been 

 suggested by Loeb and von Knaffle-Lenz that the formation of the fer- 

 tilization-membrane is accompanied by the entry of water into the egg. 

 This is prevented or delayed by the presence of colloids in the sur- 

 rounding medium because they cannot penetrate the egg and hence 

 exert an osmotic pressure tending to withdraw water from the egg. 

 For similar reasons cytolysis is also inhibited and it has also been 

 stated by B. Moore that the action of Hemolytic Agents in liquefying 

 blood-corpuscles is similarly inhibited by proteins. 



The normal concentration of protein in blood-serum lies between 

 7 and 8 per cent, and it will be seen that this lies in the margin of the 

 concentration which inhibits membrane-formation by butyric acid 

 (and also by sperm). Hence if the oocytin content of a sample of 

 serum be low, or the concentration of serum-proteins a little above the 

 average, it will fail to cause membrane-formation even in sensitized 

 eggs. Heating the serum permits membrane-formation to occur 

 because it results in coagulating and removing the proteins, and dilu- 

 tion achieves the same result in a different way. At first, however, 

 the effect of dilution in reducing the membrane-forming power of the 

 serum more than compensates for the diminished inhibition by the 

 proteins, so that dilution of serum to one-half or one-fourth usually 

 deprives even an initially active serum of the power to induce mem- 

 brane-formation. Even when the undiluted serum is sufficiently 

 potent to overcome the inhibition of its proteins so far as to cause 

 membrane-formation, the inhibition is nevertheless operative and finds 

 expression in the prevention of the subsequent cytolysis. 



The concentration of protein in the medium bathing the eggs which 

 is required to inhibit membrane-formation . affords a quantitative 

 measure of the potency of the fertilizing agent. The more concentrated 

 a solution of Saponin, for example, the greater the amount of Ovo- 

 mucoid which must be added to it to prevent the formation of mem- 

 branes. From this it is evident that the "charge" of membrane- 

 forming agent which the spermatozoon carries into the egg must be 

 less than that which is deposited upon sensitized eggs in an active serum 



