VI 



ON THE NATURE OF THE PROCESS OF FERTILIZATION^ 



I 



Experimental biology is a very recent science. Not until 

 recently have biologists begun to become conscious of the 

 uncertainty of conclusions which are not tested and verified by 

 adequate experiments. 



Leeuwenhook demonstrated in 1677 the existence of motile 

 elements in the sperm, the so-called spermatozoa. He believed 

 that the spermatozoa represented the future embryo. The 

 majority of his contemporaries assumed that the spermatozoa 

 were parasitic organisms which had nothing to do with fertiliza- 

 tion. The idea that spermatozoa are not parasites did not 

 subside until it was proved about 160 years later that the 

 spermatozoa originate from the cells of the testes. 



That sperm was needed to bring about fertilization of the 

 egg was too obvious a fact to escape even those biologists who 

 never made an experiment, but that the spermatozoa and not 

 the liquid constituents were the essential element in the sperm 

 was a fact which could not be established except experimentally. 

 It was generally assumed that no direct contact between sperm 

 and egg was necessary and that something volatile contained 

 in the sperm, the imaginary ''aura seminalis" was sufficient 

 for the act of fertilization. That contact between sperm and 

 egg was really necessary for fertilization was at last proved 

 experimentally by Jacobi (1764) who showed that fish eggs 

 can only be fertilized if the sperm is brought into direct con- 

 tact with the eggs; and by Spallanzani who put the males of 

 frogs during the act of cohabitation into trousers and convinced 



1 Reprinted, from Biological Lectures delivered at Woods Hole, 1899, by 

 courtesy of Ginn & Co., Boston. 



113 



