SPECIFICITY IN GENERIC AND SPECIFIC CHARACTERS. 325 



globin and the CO-hemoglobin are both dimorphous, and the homologous 

 forms are very nearly alike, as may be seen by comparing some of their 

 characters: 



a-oxyhemoglobin, orthorhombic, axial ratio 0.7467 1 : 0.4097 



o-CO-hemoglobin, orthorhombic, axial ratio 0.7332 1 : 0.4106 



/3-oxyhemoglobin, monoclinic, axial ratio 1.600 : 1 i, /3 = 72, a A a = 13 



^-CO-hemoglobin, monoclinic, axial ratio 1.664 : 1 t, /i = 68, a A a = 15 



Other examples of crystallographic differences in these five substances 

 examined may be found by reference to the tabulations of crystallographic 

 characters of the hemoglobins, given at the end of each chapter in which the 

 hemoglobins of the species are described. 



It will be seen therefore that not only is it possible for several different 

 kinds of oxyhemoglobin, metoxyhemoglobin, reduced hemoglobin, CO- 

 hemoglobin, and methemoglobin to occur in the same species, but that these 

 five different substances may be distinguished from each other by crystallo- 

 graphic characters as well as by spectroscopic examination. 



SPECIFICITY IN GENERIC AND SPECIFIC CHARACTERS. 



Constancy of generic characters: 



The crystals of the species of any genus belong to the same crystallo- 

 graphic system and generally to the same crystallographic group; and 

 they have approximately the same axial ratios, or their ratios are in simple 

 relation with each other. In other words, the hemoglobin crystals of any 

 genus are isomorphous. In some cases this isomorphism may be extended 

 to include several genera, but this is not usually the case, unless, as in the 

 case of the dogs and foxes for example, the genera are very closely related. 

 Isomorphism implies, however, more than mere correspondence of crystal 

 system and axial ratio. The members of an isomorphous group have 

 approximately the same forms of structure; they should, as a consequence, 

 have approximately the same constitution. Any of the genera that are rep- 

 resented by a number of species may be taken as examples of this isomorph- 

 ism of the hemoglobin crystals from the blood of animals of the same genus. 

 Such are, for example, the genera Felis, Canis, Papio, each of which is repre- 

 sented by a number of species, but to which may be added closely related 

 genera, which by some zoologists are united with these genera, as Felis 

 and Lynx, Canis and Vulpes and Urocyon. Other genera in which a smaller 

 number of species were examined show the same isomorphism, as for instance 

 the genera Mus, Sciurus, Cervus, Ovis, etc. Where several kinds of oxy- 

 hemoglobin occur in one species of a genus they are to be looked for in other 

 species of the same genus, and if the conditions are favorable they can 

 presumably all be developed in each species. These genera have crystals 

 that are isodimorphous or isotrimorphous, a more exact test of the generic 

 specificity. For example, the genus Papio has three forms of oxyhemo- 

 globin, and, as regards this substance, the hemoglobin crystals of this genus 

 are isotrimorphous. 



The oxy hemoglobins of the genus Canis, with those of the related genera 

 Vulpes and Urocyon, form a very remarkable isomorphous group in which the 

 variation in the axial ratio between the oxyhemoglobin crystals of the most 



