54 Chemical Basis of Genus and Species 



io c.c. of serum of a mammal three drops of defibrinated 

 blood of a foreign species are added and the whole is 

 exposed in a test tube to a temperature of 38°C. for 

 fifteen minutes the blood cells contained in the added 

 blood are all cytolyzed; that this, however, does not 

 occur so rapidly when the blood of a related species is 

 used. He could thus show that human blood serum 

 dissolves the erythrocytes of the eel, the frog, pigeon, 

 hen, horse, cat, and even that of the lower monkeys 

 but not that of the anthropoid apes. The blood of the 

 chimpanzee and of the human are no longer incom- 

 patible, and this discovery was justly considered by 

 Friedenthal as a confirmation of the idea of the evolu- 

 tionists that the anthropoid apes and the human are 

 blood relations. x 



This line of investigation had in the meanwhile 

 entered upon a new stage when Kraus, Tchistowitch, 

 and Bordet discovered and developed the precipitin re- 

 action, which consists in the fact that if a foreign serum 

 (or a foreign protein) is introduced into an animal the 

 blood serum of the latter acquired after some time 

 the power of causing a precipitate when mixed with 

 the antigen, i. e., with the foreign substance originally 

 introduced into the animal for the purpose of causing 

 the production of antibodies in the latter; while, of 

 course, no such precipitation occurs if the serum of a 



1 Friedenthal, H., "Experimenteller Nachweis der Blutverwandt- 

 schaft." Arch.f. Physiol., 1900, 494. 



