44 



SCIENCE 



[N. iS. Vol. XLIII. No. 1098 



In their subsequent publications they 

 concluded that it is 



infinitely probable that the number of animalcules 

 employed in fertilization corresponds to that of 

 the embryos developed ... so that the action of 

 these animalcules which we regard as the male 

 reproductive elements is individual, not collective. 



They concluded that a spermatozoon pen- 

 etrates each egg and becomes "the rudi- 

 ment of the nervous system, and that the 

 membrane (germ disc 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 et Dumas were essentially cor- 

 rect, while others still adhered to the idea 

 that the fluid part of the seminal fluid was 

 the fertilizing medium. Thus the cele- 

 brated embryologist Bischoff in 1842 does 

 not hesitate to declare outright for the lat- 

 ter 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 maintain- 

 ing its chemical composition is relegated to the 

 movements of the spermatozoa. 



However, Bischoff subsequently became 

 convinced that the spermatozoa were them- 

 selves the essential agents, though he still 

 refused to believe in the penetration of the 

 egg. KoUiker had put forward a contact 

 theory of fertilization, which Bischoff re- 

 garded merely as a statement of facts re- 

 quiring further development. He there- 

 fore adopted the idea of catalyzers, at that 

 time a new idea in chemistry, and held that 

 the spermatozoon was essentially a catalytic 

 agent, i. e., as he defined it, "a form of mat- 

 ter characterized by definite transformation 



and internal movement" which it transmits 

 by contact to the egg, which is in a condi- 

 tion of maximum tension or inclination to 

 assume the same form of transformation 

 and movement. Fertilization is thus not 

 a process of union and fusion as in ordinary 

 chemical combination, but a catalytic proc- 

 ess, as defined above. 



This point of view deserves to be empha- 

 sized as one of the first attempts at a phys- 

 ico-chemical explanation of fertilization. 



For some time naturalists were divided 

 between the two points of view, viz., that 

 of Prevost et Dumas, that the sperm pene- 

 trated into the egg, and that of Kolliker and 

 Bischoff that it acted by contact. Lalle- 

 mand (1841) well expresses the view of 

 those who believed in the union of the ovum 

 and spermatozoon : 



Each of the sexes furnishes material already 

 organized and living. ... A fluid obviously can 

 not transmit form and life which it does not pos- 

 sess. . . . Fertilization is the union of two liv- 

 ing parts which mutually complete each other and 

 develop in common. . . . When one embraces in a 

 single point of view the reproduction of all living 

 beings, one arrives at the following more general 

 formula: Eeproduetion is the separation of a liv- 

 ing part which may either develop separately or 

 acquire from another living part the supplemen- 

 tary elements necessary for the ulterior develop- 

 ment of a being similar to the type. . . . The 

 preservation of the type is due to the extension of 

 the same act which has produced the development 

 of each individual being. 



This is the most complete statement of 

 the principle of genetic continuity that I 

 have found in the literature of this period. 



These observations and conclusions were 

 found on the eve and early morrow of the 

 greatest biological generalization, the cell- 

 theory. Though Schwann interpreted the 

 ovum as a cell (1838), this view did not at 

 once become dominant, and was generally 

 accepted only after over twenty years of 

 discussion. The view that spermatozoa 

 were parasitic organisms was more or less 



