SPECIFIC EXCITATORY FORCES 37 



remains inactive, if it were not that the specific excitation A^, 

 corresponding to the determinant A, exercises a greater influ- 

 ence on the cell than the specific excitation B^, corresponding 

 to determinant B ? The nature of this specific stimulus we do 

 not know, just as we do not know the intricate nature of the 

 nutritive changes in metabolism. But what else could explain, 

 for instance, the phenomenon of sexual dimorphism ? The 

 existence, not only of primary, but also of secondary sexual 

 characters, compels us to accept the hypothesis of the presence 

 of two sets of determinants in the germ-plasm. We know that 

 even so subtle a character as the soprano voice of a woman 

 can be handed down through the son to the grand-daughter. 

 Obviously, then, it must have remained in an inactive or latent 

 condition in the germ-plasm of the son. In the case of certain 

 animals, such as the Aphides and the Daphnids, females only are 

 produced for numerous generations in succession ; and the deter- 

 minants of the male sex must remain inactive throughout these 

 generations, for they develop into activity after a certain time, 

 and a male is born. What is this renewed activity of the male 

 determinants after so many generations of inactivity but a re- 

 assertion of their specific excitatory force ? 



We come now to the question of the number of the deter- 

 minants. Are the determinants in some cases identical with 

 the biophors, which in other cases go to make up the deter- 

 minant ? In the case of very simple organisms this identity 

 may obtain, but it is not general. The determinants may be 

 defined as particles of the germinal substance which determine 

 the function and structure of every part of the body that is 

 capable of independent variation and inheritance. In other 

 words, it is the pressure of specific determinants in the germ- 

 plasm that determines the definition of a cell or group of cells 

 in a specific manner. As to the number in which such deter- 

 minants are present in the organism, this will depend on the 

 degree of complexity which the organism exhibits. In the case 



