The Organism and its Chemistry 97 



stances that show differences in crystallographic structure 

 are different chemical substances" ^^ is accepted. 



As far as the conditions of the researches would permit, 

 the crystals of oxyhemoglobin were made the standard of 

 comparison. When several forms of this are obtained from 

 the same blood "eacli form, A-oxyhemoglobin, B-oxyhemo- 

 globin, etc., appears always in its own proper form and 

 axial ratio when the blood of different individuals of the 

 same species are examined. The same is true of the 

 other hemoglobins — metoxyhemoglobin, reduced hemoglobin, 

 methemoglobin ; so that the hemoglobins of any species are 

 definite substances for that species. But upon comparing 

 the corresponding substances in different species of a genus 

 it is generally found that they differ the one from the other 

 to a greater or less degree ; the differences being such that 

 when complete crystallographic data are available, the dif- 

 ferent species can be distinguished by these differences in 

 their hemoglobins. As these hemoglobins crystallize in iso- 

 morphous series, the differences between the angles of the 

 crystals of the species of a genus are not, as a rule, great; 

 but they are as great as is usually found to be the case 

 with minerals or chemical salts that belong to an isomor- 

 phous group." ^^ In illustration we may select the table 

 for the species of cats studied, this being based on the crys- 

 tals of reduced hemoglohi/n. Tlie crystals belong to the 

 orthorhombic system and are optically positive for all the 

 species, so these items need not appear in the table. 



