CRYSTALLINE FORMS OF HEMOGLOBIN 357 



per cent, of Ammonium Oxalate to freshly shed blood, which not only 

 prevents clotting but accelerates the process of crystallization, then 

 lake the corpuscles by shaking up the blood with ether, remove the 

 debris of corpuscles by centrifugalization and allow the fluid to evapo- 

 rate on a microscopic slide. In some cases the nature of the agent em- 

 ployed to lake the blood or induce Hemolysis is of importance in deter- 

 mining the ease of crystallization. Thus if dogs' blood be laked with 

 Toluol, an abundance of crystals of hemoglobin is easily obtained by 

 merely cooling the laked blood in a refrigerator. 



The results of Reichert and Brown have shown that the crystals 

 obtained from the blood of different species are never identical in 

 form. From an enormous number of measurements of crystal-angles, 

 etc., conducted upon hemoglobins derived from a very wide variety 

 of species these observers conclude that the crystals of the different 

 species of any one genus belong to the same crystallographic system 

 and generally to the same crystallographic group, and they have 

 approximately the same axial ratios, or their ratios bear a simple 

 relation to each other. In other words the hemoglobin crystals of 

 any genus are isomorphous, but not identical. In some cases this 

 Isomorphism may be extended to include several genera, but this is 

 usually not the case unless, as in the case of the dogs and foxes, for 

 example", the genera are very closely related. On the other hand the 

 oxyhemoglobin obtained from the same species always crystallizes in 

 the same form, although often with a different "habit" when obtained 

 by different methods of preparation. But upon comparing the hemo- 

 globins from different species of a genus it is always found that they 

 differ from one another to a greater or less degree in angles or axial 

 ratio, in optical characters, and particularly in those characters com- 

 prised under the general term "Crystal Habit," so that one species can 

 usually be distinguished from another by the form of its hemoglobin 

 crystals (Fig. 21). 



A clear relationship is thus seen to subsist between the physico- 

 chemical behavior of a constituent of organisms, and their place in the 

 phylogenetic scale of relationships as established by their gross mor- 

 phology, and a long stride has been taken toward the establishment of 

 a physicochemical basis for morphological distinction. The further, 

 and entirely independent question now arises, however, as to the 

 chemical origin of the observed physicochemical phenomena. 



Our experience with the crystallography of inorganic and the 

 simpler organic substances has led us to infer with a considerable 

 degree of confidence that substances which show differences in crystal- 

 lographic structure are different chemical substances. Crystal form 

 is affected even by isomeric modifications which analysis, unaided by 

 other methods of investigations, fails to reveal. Now the enormous 

 number of atoms in a protein molecule encourages, at first sight, the 

 supposition that an enormous and indeed, for all practical purposes, 

 an infinite number of isomerides are possible between which the most 

 refined methods of analysis would not enable us to distinguish, but 



