76 THE BIOLOGICAL PROBLEM OF TO-DA Y 



amphibia ; from these he drew ' the inference, 

 important for classification of animals, that those 

 animals anatomically most nearly allied have their 

 blood most closely alike.' In fact, ' the destruction 

 of the foreign blood happens the more slowly the 

 more nearly the animals are allied.' ' Thus, in 

 doubtful cases, experiments on transfusion might 

 settle degrees of relationship. Between individuals 

 of the same species transfusion is a complete 

 success ; when the species are closely allied, the 

 transfused blood disappears only very gradually, 

 and large quantities may be transfused without 

 harm. The further apart the animals may be, in 

 a system of classification, the more violently the 

 destruction of the foreign blood takes place, and 

 the smaller is the quantity that can be endured in 

 the vessels. Thus, in the extent to which blood 

 transfusion may occur, I see a step towards the 

 foundation of a Darwinian theory applied to cells.' 



As yet, transplantations and transfusions between 

 animals of different species have been considered 

 with a view to their importance in surgery and in 

 medicine, rather than from their purely physio- 

 logical side. From the results given above, in 

 which I believe, although there might be drawn 

 from literature contradictory results in which, 

 however, I cannot feel confident I am prepared 

 to extend a conclusion to the animal kingdom that 

 is better supported in botany : the conclusion that 

 the cells and tissues possess, in addition to their 

 definite microscopical characters, more general, in- 

 trinsic, specific characters, and that one may speak 



