64 Chemical Basis of Genus and Species 



are therefore the bearers of the specificity of Hving 

 organisms. 



Bradley and Sansum' found that guinea-pigs sensi- 

 tized to beef or dog hemoglobin fail to react or react but 

 slightly to hemoglobin of other origin. The hemoglo- 

 bins tried were dog, beef, cat, rabbit, rat, turtle, 

 pig, horse, calf, goat, sheep, pigeon, chicken, and 

 man. 



6. It would be of the greatest importance to show 

 directly that the homologous proteins of different 

 species are different. This has been done for hemo- 

 globins of the blood by Reichert and Brown, =" who have 

 shown by crystallographic measurements that the 

 hemoglobins of any species are definite substances for 

 that species. 



The crystals obtained from different species of a genus 

 are characteristic of that species, but differ from those of 

 other species of the genus in angles or axial ratio, in optical 

 characters, and especially in those characters comprised 

 under the general term of crystal habit, so that one species 

 can usually be distinguished from another by its hemoglobin 

 crystals. But these differences are not such as to preclude 

 the crystals from all species of a genus being placed in an 

 isomorphous series (p. 327). 



' Bradley, H. C, and Sansum, W. D., Jour. Biol. Chem., 1914, xviii., 

 497. 



"Reichert, E. T., and Brown, A. P., "The Differentiation and Speci- 

 ficity of Corresponding Proteins and other Vital Substances in Relation 

 to Biological Classification and Organic Evolution." Carnegie Insti- 

 tution Publication No. 116, Washington, 1909. 



