igoS] A CRYSTALLOGRAPHIC STUDY OF THE HEMOGLOBINS. 299 



is usually the case with minerals in rock sections. Measurements 

 within the limit of error of the instrument could frequently be ob- 

 tained, and, as various orientations were available, the results of 

 the angular measurements often furnished complete data for the 

 calculation of the axial ratios. The crystals examined were usually 

 complete and often geometrically perfect, so that the symmetry and 

 crystal habit could be determined as readily as in the case of ordi- 

 nary mineral substances occurring in isolated crystals. 



A chemical substance, possessing a rational composition, tends 

 to arrange its parts in an orderly manner so that a definite struc- 

 ture is assumed, which results in a definite external form. This is 

 so universally true that the crystalline condition is the normal one 

 for matter of definite composition. Differences of crystalline form 

 hence indicate differences of substance; and, by the crystallographic 

 method of investigation, obscure dift'erences, such as those between 

 isomerides, may readily be detected. 



Photographic records of the crystals were secured and upwards 

 of 2,500 negatives have been made. The hemoglobins of more than 

 one hundred species have been examined and data secured in regard 

 to their crystals. From a study of these records certain facts stand 

 out very prominently. 



I. Tlic Constancy of Generic Characters in the Crystals. — The 

 crystals of the species of any genus belong to a crystallographic 

 group. When their characters are tabulated, they at once recall 

 the crystallographic groups of minerals. The crystals of the genus 

 Felis form an isomorphous group ; as strictly isomorphous, in fact, 

 as the group of the rhombohedral carbonates among minerals. The 

 genus Canis is even more strictly isomorphous, but the crystals of 

 hemoglobin from the two genera are perfectly distinct, the one from 

 the other. 



As an example of the individuality of these generic characters 

 the following may be cited : A sample of blood, marked as that of 

 a certain species of baboon was received from one of our Zoological 

 Gardens. Upon making preparations and examining the crystals, it 

 w^as at once evident that they did not correspond to any species of 



