432 BLOOD AND LYMPH. 



slide for examination. According to Reichert, the deposition of the 

 crystals is hastened by adding ammonium oxalate to the blood in 

 quantities sufficient to make from 1 to 5 per cent, of the mixture. 

 In man and in most of the mammalia hemoglobin is deposited in 

 the form of rhombic prisms; in the guinea-pig it crystallizes in 

 tetrahedra (d, Fig. 181); in the rat in the form of elongated six- 

 sided plates, and in the squirrel in hexagonal plates. In an elabo- 

 rate and careful study of the crystallographic characters of hemo- 

 globin from a large number of animals Reichert and Brown* have 

 shown that differences exist between the crystals of various species 

 of such a character that they may be used to determine whether or 

 not animals belong to the same genus. This difference in crystal- 

 line form implies some difference in molecular structure, and taken 

 together with other known variations in property shown by hemo- 

 globin from different animals leads us to believe that the huge mole- 

 cule has a labile structure, and that it may differ somewhat in its 

 molecular composition or atomic arrangement without losing its 

 physiological property of an oxygen-carrier. In this connection 

 it is interesting to state that the hemoglobin of horses' blood, which 

 crystallizes ordinarily in large rhombic prisms, may be made to give 

 hexagonal crystals by allowing it to undergo putrefaction, and that 

 the form of the crystals may then be changed from hexagons to 

 rhombs by varying the temperature of the solutions. f The crystals 

 are readily soluble in water, and by repeated crystallization the 

 hemoglobin may be obtained perfectly pure. As in the case of 

 other soluble protein-like bodies, solutions of hemoglobin are 

 precipitated by alcohol, by mineral acids, by salts of the heavy 

 metals, by boiling, etc. Notwithstanding the fact that hemoglobin 

 crystallizes so readily, it is not easily dialyzable, behaving in this 

 respect like non-crystallizable colloidal bodies. The compounds 

 which hemoglobin forms with carbon monoxid (CO) and nitric oxid 

 (NO) are also crystallizable, the crystals being isomorphous with 

 those of oxy hemoglobin. 



Absorption Spectra. Solutions of hemoglobin and its deriv- 

 ative compounds, when examined with a spectroscope, give 

 distinctive absorption bands. 



Light, when made to pass through a glass prism, is broken up into its 

 constituent rays, giving the play of rainbow colors known as the spectrum. 

 A spectroscope is an apparatus for producing and observing a spectrum. A 

 simple form, which illustrates sufficiently well the construction of the appara- 

 tus, is shown in Fig. 182, P being the glass prism giving the spectrum. Light 

 falls upon this prism through the tube (A) to the left, known as the "colli- 

 mator tube." A slit at the end of this tube (S) admits a narrow slice of light 

 lamplight or sunlight which then, by means of a convex lens at the other 

 end of the tube, is made to fall upon the prism (P) with its rays parallel. In 



* Reichert and Brown, " The Crystallography of Hemoglobins," Carnegie 

 Institution of Washington, No. 116, 1909. 



t Uhlik, "Archiv f. d. gesammte Physiologic," 104, 64, 1904. 



