OTHER EXPERIMENTS ON HEREDITY 375 



how far they may be found to apply in the breeding of pure 

 strains. 



No one can say at present that Mendelian inheritance is con- 

 spicuously illustrated in what we know of inheritance in horses, 

 dogs, and man. Yet, it is quite conceivable that Mendelian 

 inheritance may be demonstrated in horses, dogs, and man — in 

 cases where the parents do not contain a medley of latent strains, 

 but are sharply contrasted with one another in respect to one 

 or more unit characters. The danger is of trying to universalize 

 the Mendelian formula, and some of the attempts that have 

 been made to give a Mendelian interpretation to discrepant 

 facts seem to us very far-fetched. On the face of it, when we 

 remember all the possible variables, it seems very unlikely 

 that there should be only one mode of inheritance — and that 

 Mendelian. 



There is, we think, much reason to believe that in some cases 

 the unit characters are represented in the germ-plasm by deter- 

 minants which are very stable in themselves, which must be 

 everything or nothing in the hypothetical struggle antecedent 

 to and associated with development, whose expression will not 

 blend with, or even allow of the expression of contrasted analo- 

 gous determinants. There is, we think, equal reason to believe 

 that in other cases the unit-characters are not so " exclusive," 

 but may combine with analogous unit-characters to form a blend 

 or a particulate mosaic. 



As was to be expected, the discoveries of the Mendelian 

 experimenters have raised problems in solving others, and 

 various elaborations have been found necessary in order to 

 bring or keep certain phenomena within the scope of Mendelian 

 interpretation. It may be that some of the subtleties of for- 

 mulation are necessary and transitional ; it may be that some 

 of the difficulties are due to over-stretching the Mendelian 

 concepts. 



One of the active experimenters has given expression to this. 



