PHYSICOCHEMICAL DIFFERENTIATION 79 



the same species, but also between different sets of families 

 which constitute a strain, for certain chemical characters dif- 

 ferentiate them from other strains of the same species. It 

 has been shown, for instance, that white mice bred in Europe 

 differ chemically from white mice bred in America, although 

 the appearance of both strains may be identical." 



The investigations of Reichert and Brown (cited in Chapter 

 VIII, p. 247) give an insight into the almost inconceivable 

 physicochemical complexity of a single element of the blood, 

 namely, the oxyhemoglobin crystals. 



