10 PROBLEMS OF FERTILIZATION 



They concluded that a spermatozoon penetrates 

 each egg and becomes "the rudiment of the nervous 

 system, and that the membrane (germ disk of the egg) 

 in which it is implanted furnishes, by the diverse 

 modifications which it undergoes, all the other organs of 

 the embryo. ' 



These studies gave a new impetus to the study of 

 fertilization; some were convinced that Prevost and 

 Dumas were essentially correct, while others still adhered 

 to the idea that the fluid part of the seminal fluid was 

 the fertilizing medium. Thus the celebrated embry- 

 ologist Bischoff in 1842 does not hesitate to declare 

 outright for the latter view, "that only the dissolved 

 part of the semen penetrates into the egg and thus 

 completes fertilization. ' He considered that 



Valentin's hypothesis united all the facts: the seminal fluid is so 

 unstable chemically as to break down as soon as the particles 

 come to rest; it is similar to the blood in this respect, but it is not 

 in regular circulation and the function of maintaining its chemical 

 composition is relegated to the movements of the spermatozoa. 



However, Bischoff subsequently became convinced 

 that the spermatozoa were themselves the essential 

 agents, though he still refused to believe in the pene- 

 tration of the egg. Kolliker had put forward a contact 

 theory of fertilization, which Bischoff regarded merely 

 as a statement of facts requiring further development. 

 He therefore adopted the idea of catalyzers, at that 

 time a new idea in chemistry, and held that the sperma- 

 tozoon was essentially a catalytic agent, i.e., as he defined 

 it, "a form of matter characterized by definite trans- 

 formation and internal movement' which it transmits 

 by contact to the egg, which is in a condition of maximum 



