THE PROCESS OF FERTILIZATION, 275 



think that this objection is valid. We know that simple varia- 

 tions in the configuration of a molecule have an enormous 

 effect upon life phenomena. This is shown among others by 

 the work of Emil Fischer on the relation between the molecu- 

 lar configuration of sugars and their fermentability. When 

 Miescher made his experiments he was not familiar with such 

 possibilities. Moreover, Miescher was not able to state whether 

 the spermatozoa contain enzymes or not. 



A third theory was a physical theory (Bischof ). This theory 

 assumes that a peculiar condition of motion exists in the sper- 

 matozoon which is transmitted to the egg and causes its devel- 

 opment. It should be said, however, that this idea is not so 

 very different from the chemical conception, because it assumes 

 exactly the same for the spermatozoon that Liebig assumes for 

 the enzymes. Liebig thought that the enzymes owed their 

 power of producing fermentation to the motions of certain 

 atoms or groups of atoms. 



The fourth conception is the stimulus conception, which was 

 originated by His. According to this conception the egg is 

 considered as a definite machine which if once wound up will 

 do its work in a certain direction. The spermatozoon is the 

 stimulus which causes the egg to undergo its development. It 

 is to be said in connection with this stimulus conception that 

 the main point at issue is omitted, as to whether the stimulus 

 carried by the spermatozoon is of a physical or a chemical char- 

 acter, and in this way, of course, the stimulus conception is 

 nothing but a disguised repetition of the chemical or physical 

 theory of fertilization. 



All these theories are so vague that we do not need to be 

 surprised that none of them has led to any further discovery. 

 If we want to make new discoveries in biology, we must start 

 from definite facts and observations, and not from vague spec- 

 ulations. Among these observations the most important are 

 those on parthenogenesis. It had been observed for a long 

 time that the unfertilized egg of the silkworm can develop par- 

 thenogenetically. It was, moreover, known that plant lice can 

 give rise to new generations without fertilization. The most 

 impressive fact concerning the parthenogenesis of animals was 



