280 A THEORY OF HEREDITY . VIII 



and accumulate in sperm-cells and germ-cells, we may 

 substitute tlie theory of transmission of force, the two 

 theories standing to one another in the same relation 

 as the emission and undulatory theories of light. 



It may, however, be very fairly questioned whether 

 our conceptions of the vibrations of complex molecules, 

 or in other words, their force-affections, are sufficiently 

 advanced to render it desirable to substitute the 

 vaguer though possibly truer undulatory theory of 

 heredity for the more manageable molecular theory 

 (Pangenesis). How are we to conceive of the propa- 

 gation of such states of force-affection or vibration 

 (as they are vaguely termed) through the organism 

 from unit to unit ? In what manner, again, are we 

 to express the dormancy of the pangenetic gemmules 

 in terms of molecular vibration ? It is true that 

 molecular physics furnishes us with some analogies in 

 the matter of the propagation of particular states of 

 force-affection from molecule to molecule, as, for 

 example, in the various modes of decomposition ex- 

 hibited by gun-cotton, in contact actions and the 

 like ; but it will require a very extended analysis of 

 both the phenomena of heredity and of molecular 

 phenomena similar to those just cited, to enable us 

 to supersede the admittedly provisional hypothesis of 

 Pangenesis by a hypothesis of vibrations. And it is 

 necessary here to remark that in the fundamental 

 conception of Pangenesis, namely, the detachment 

 from the living cells of the organism of gemmules 

 which then circulate in the organism, there is nothing 

 contrary to analogy, but rather in accordance with it. 



