Chemical Basis of Genus and Species 53 



different species are mixed and when incompatibility 

 exists between varieties, as is the case in the graft on 

 mammals. 



//. The Chemical Basis of Genus and Species and of 



Species Specificity 



4. Fifty or sixty years ago surgeons did not hesitate 

 to transfuse the blood of animals into human beings. 

 The practice was a failure, and Landois' showed by 

 experiment that if blood of a foreign species was intro- 

 duced into an animal the blood corpuscles of the trans- 

 fused blood were rapidly dissolved and the animal into 

 which the transfusion was made was rendered ill and 

 often died. The result was different when the animals 

 whose blood was used for the purpose of transfusion 

 belonged to the same species or a species closely related 

 to the animal into which the blood was transfused. 

 Thus when blood was exchanged between horse and 

 donkey or between wolf and dog or between hare and 

 rabbit no hemoglobin appeared in the urine and the 

 animal into which the blood was transfused remained 

 well.^" This was the beginning of the investigations 

 in the field of serum specificity which were destined to 

 play such a prominent role in the development of medi- 

 cine. Friedenthal was able to show later that if to 



^ Landois, L., Zur Lehre von der Bluttransfusion. Leipzig, 1875. 

 » This is probably true only within the limits of exactness used in 

 these experiments. 



