INTRODUCTION. 



and in the primary dissociation products in both percentage and groups, 

 seem to be conclusive that these substances (assuming their purity) are not 

 identical. If Griffiths's work on the achroglobulins be confirmed, we have 

 another such instance. Other indications of differentiation are shown in the 

 difference in the globin of the horse, bullock, and dog on the one hand and 

 that of the goose on the other; the "precipitin test," by which can readily 

 be shown certain zoological differentiations of the blood, milk, and flesh 

 extracts, is admitted to depend upon specificities of proteins; hemoglobins 

 of different species are recorded as differing in solubility, decomposability, 

 water of crystallization, crystallizability, color intensity, and absorptive 

 power in relation to and C0 2 ; in contradiction to Hiifner, who describes 

 such a striking identity and constancy of the extinction coefficients and 

 quotients of the oxyhemoglobin of all species, we have sufficient evidence in 

 literature to show that these coefficients do vary in different species. Differ- 

 ences have been noted in several hemocyanins in regard to the degree of 

 dissociability of the and C0 2 , and to the temperature of coagulation; and 

 there are indications of differences in echinochromes and chlorocruorins. 



If chemical differences exist in corresponding proteins they seem to be 

 of so subtle a nature, except in rare instances, as to be beyond the possi- 

 bilities of the present methods of chemical distinction. It was therefore 

 believed that some other method might bring success where the chemist 

 has failed. As it is recognized that crystalline form may depend upon 

 either chemical composition or constitution, it seems that the method of 

 investigating microscopic crystals as developed by Sorby, and later by 

 Zirkel, Rosenbusch, and others, and the resulting lithological microscope 

 with its various attachments, might afford the means of obtaining satis- 

 factory results. By this method of investigation an entire science, the 

 science of petrography, has been built up. The "optical reactions" thus 

 obtained are often as distinctive, and even as exact, as the chemical re- 

 actions, and this instrument is now used by the petrographer and chemist 

 alike for the study of crystals too small to be examined in the usual way. 

 Thus the crystals may be studied in the solution in which they are formed, 

 and fairly accurate measurements may be obtained of their plane angles 

 and various optical properties. Inasmuch as the optical properties, which 

 are dependent upon the internal tensions of the crystal, are often more 

 distinctive than the exterior form, and since even "isomeric substances 

 possess different crystal structures" (Groth), it will be readily seen that 

 this method of investigation may show differences which at present may 

 be or are too obscure for the chemist. 



Thus far only a very limited number of the proteins have been obtained 

 in crystalline form. A number of hemoglobins and hemoglobin compounds 

 and derivatives, serum albumin, lactalbumin, casein, vitellin, a number of 

 globulins from seeds and nuts (some of them being recorded as albumins), 

 the albumin and globulin of egg-white, hyalin, two proteins from abnormal 

 urines (one of which is a casein-like body and the other probably a hetero- 

 proteose), ichthulin (probably a lecithoprotein) from the eggs of fish, gluto- 

 kyrin, hemocyanin, and phycoerythrin and phycocyanin of algse, include 



