652 



SCIENCE 



[N. S. Vol. XL. No. 1036 



stance or a combination of substances may 

 exist in the form of heterogeneous or homo- 

 geneous systems, a heterogeneous system con- 

 sisting of a number of homogeneous systems, 

 each of which latter is a manifestation of an 

 individual phase and distinguishable from the 

 others by physical, mechanical, chemical or 

 physiological properties. The number of 

 phases of a heterogeneous system increases 

 with the number of component systems, and 

 the number of the latter is in direct relation- 

 ship to the number of independent variable 

 constituents. Therefore, by means of varia- 

 tions of either or both intramolecular or extra- 

 molecular arrangement the number of forms of 

 a substance or combination of substances may 

 range from few to infinite. 



Our means of differentiating stereoisomers 

 are, on the whole, limited, and for the most 

 part crude, and while it has been found that 

 differences so marked as those referred to may 

 be detected by the ordinary procedures, it seems 

 obvious that the inherent limitations of such 

 methods render them inadequate where a large 

 number of stereoisomerides or related bodies 

 which may exhibit only obscure modifications 

 are to be definitely differentiated, so that 

 other and more sensitive methods must be 

 sought, or at least special methods that are 

 adapted to exceptional conditions. The re- 

 sults of much preliminary investigation in 

 this direction led in one research to the adop- 

 tion of the crystallographic method, especially 

 the use of the polarizing microscope, which 

 in its very modem developments of analysis 

 has demonstrated that substances which have 

 different molecular structures exhibit corre- 

 sponding differences in crystalline form and 

 polariscopic properties; and, moreover, that 

 the " optical reactions " may be found to be as 

 distinctive and as exact analytically as the 

 reactions obtained by the conventional methods 

 of the chemist. Furthermore, the necessities 

 of the hypothesis demanded the selection of a 

 substance for study of a character which upon 

 theoretical grounds might be expected to exist 

 in nature widely distributed and readily pro- 

 curable, and, as a consequence, hemoglobin 

 was selected. 



In the investigation of the hemoglobins I 

 had as a coworker Professor Amos Peaslee 

 Brown. Hemoglobins were examined that were 

 obtained from over 100 animals, representing 

 a large variety of species, genera and families. 

 From the data recorded certain facts are 

 especially conspicuous, among which may b© 

 mentioned the following: 



1. The constant recurrence of certain angles, 

 plane and dihedral, in the hemoglobins of 

 various species, even when the species are 

 widely separated and the crystals belong to 

 various crystal systems. This feature indi- 

 cates a common structure of the hemoglobin 

 molecules, whatever their source. 



2. The constant recurrence of certain tjnpes 

 of twinning in the hemoglobins, and the prev- 

 alence of mimosie. This has the same signif- 

 icance as the foregoing. 



3. The constancy of generic characters in 

 the crystals. The crystals of the various spe- 

 cies of any genus belong to a crystallographic 

 group. When their characters are tabulated 

 they at once recall crystallographic groups of 

 inorganic compounds. The crystals of the 

 genus Felis constitute an isomorphous group 

 which is as strictly isomorphous as the groups 

 of rhombohedral and orthorhombic carbonates 

 among minerals, or the more complex mole- 

 cules of the members of the group of mono- 

 symmetric double sulphates. 



4. The crystallographic specificity in rela- 

 tion to species. The crystals of each species of 

 a genus, when they are favorably developed 

 for examination in the polarizing microscope, 

 can usually be distinguished from, each other 

 by definite angles and other properties, while 

 preserving the isomorphous character belong- 

 ing to the genus. Where, on account of diffi- 

 culty of measurement, the differences can not 

 be given a quantitative value variations in 

 habit and mode of growth of the crystals often 

 show si)eeific differences. 



5. The occurrence of several types of oxy- 

 hemoglobin in members of certain genera. 

 In some species the oxyhemoglobin is dimor- 

 phous and in others trimorphous. Where sev- 

 eral types of crystals occur in this way in the 

 species of a genus the crystals of each type 



