66 Chemical Basis of Genus and Species 



minerals or chemical salts that belong to an isomorphous 

 group (p. 326). 



As Professor Brown writes me, the difficulty in 

 answering the question definitely, whether or not the 

 hemoglobins of different species are chemically different, 

 lies in the fact that there is as yet no criterion which 

 allows us to discriminate between a species and a Men- 

 delian mutation except the morphological differences. 

 It is not impossible that while species differ by the con- 

 stitution of some or most of their proteins, Mendelian 

 heredity has a different chemical basis. 



It is regrettable that work like that of Reichert and 

 Brown cannot be extended to other proteins, but it 

 seems from anaphylaxis reactions that we might expect 

 results similar to those in the case of the hemoglobins. 

 The proteins of the lens are an exception inasmuch as, 

 according to Uhlenhuth, the proteins of the lens of 

 mammals, birds, and amphibians cannot be discrimi- 

 nated from each other by the precipitin reaction. 1 



7. The serum of certain humans may cause the 

 destruction or agglutination of blood corpuscles of 

 certain other humans. This fact of the existence of 

 "isoagglutinins" seems to have been established for 

 man, but Hektoen states that he has not been able to 

 find any isoagglutinins in the serum of rabbits, guinea- 

 pigs, dogs, horses, and cattle. Landsteiner found the 



1 Uhlenhuth, Das biologische Verfahren zur Erkennung und Unter- 

 scheidung von Menschen und Tierblut, Jena, 1905, p. 102. 



