130 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



determination of differences in weight amounting to pounds; similarly, 

 homoio- and syngenesiotransplantations distinguish between the finer degrees 

 of relationship of individuality differentials, whereas, heterotransplantation is 

 not quite adequate for the finer and more general distinction of species dif- 

 ferentials. 



(4) The data given also demonstrate that reciprocal transplantations, in 

 which the role of donor and host are reversed, may differ as far as the fate 

 of the transplant is concerned. We have referred already to the greater 

 severity of reactions found in some instances in the guinea pig than in the 

 rat, and we have also shown the difference in reactions in reciprocal rat- 

 mouse and C57-Peromyscus transplantations. Similar differences in reciprocal 

 transplantations may be found also in some instances in homoio- and in 

 syngenesiotransplantations. It is the host which reacts against the graft, but 

 the latter does not seriously affect the condition in the host ; the ability to re- 

 act strongly against a strange tissue differs in different species, strains, and 

 probably even individuals. 



There is one last conclusion which is of more general interest. In the case 

 of syngenesio- and homoiotransplantations we find a relatively wide range of 

 reactions in different individual experiments, in accordance with the great 

 range of variations in the combinations between different individuality dif- 

 ferentials of host and graft. In contrast to these, the range in the results of 

 heterotransplantations is rather narrow ; this is due, at least partly, to the 

 great severity of the reactions in heterogenous transplantations, which ap- 

 proaches a threshold already in the relations between nearly related species, 

 but it may also be due to the fact that the range of variation in the genetic 

 constitution of the species differentials is much smaller than that of the 

 homoiogenous differentials. 



