No. 581] ENTRANCE OF THE SPERMATOZOON 279 



the egg, whereby the fertilizin molecule undergoes a 

 change in the other end; and this change causes the egg to 

 develop. The fertilizin is thus an "amboceptor" in the 

 sense of Ehrlich's side-chain theory. 



The side-chain theory was invented by Ehrlich for an 

 altogether different purpose. Bordet had found that for 

 certain phenomena of immunity two substances were 

 needed (which Ehrlich named amboceptor and comple- 

 ment, respectively). Ehrlich assumed that they were 

 bound chemically by the antigen (the substance against 

 which the organism was immunized) but found that while 

 the antigen (A) was able to bind B (the amboceptor) in 

 the absence of C, it was not able to bind the complement 

 C in the absence of B. From this Ehrlich concluded that 

 of the two possible modes of linkage between the three 

 bodies A^, and A—B—C the latter was the one which 

 really occurred. Since in this case C is not directly 

 linked with A but through the intermediation of B he 

 called B the " amboceptor " and the scheme of linkage a 

 " side-chain " linkage. 



Lillie applies tiiis theory (which covers the two possible 

 modes of linkage of two chemical compounds to a third 

 one) to the entrance of the spennatozoon into the egg, by 

 calling the egg an antigen A and the spermatozoon a com- 

 plement C and assuming the existence of a hypothetical 

 amboceptor B in the form of the substance that causes 

 agglutination, the " fertilizin." Even if we are willing 

 to overlook the fact that the egg and the spermatozoon 

 are cells and not simple organic compounds and if we are 

 willing to overlook the further fact that the assumption 

 of an amboceptor as a connecting link between the two 

 is arbitrary we can not overlook the fact that the spenna- 

 tozoon does not combine chemically with the egg but that 

 it actually enters into the egg and attaches itself to the 

 egg nucleus. It seems then futile to discuss whether the 

 spermatozoon combines with the egg in side-chain fashion 

 (namely, Egg— Fertilizin— Spermatozoon) or in direct 



