GENERAL PROPERTIES: THE CORPUSCLES. 429 



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

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

 the form of rhombic prisms; in the guinea-pig it crystalUzes 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 b}^ 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. 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 l^odies. The compounds 

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

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

 those of oxyhemoglobin. 



Absorption Spectra. — Solutions of hemoglobin and its deriv- 

 ative compounds, when examined with a spectroscope, give 

 distinctive aljsorption 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 

 passing through the prism the rays are dispersed by unequal refraction, giving 

 a spectrum. The spectrum thus produced is examined "by the observer with 

 the aid of the telescope {B) . When the telescope is properly focused for the 

 rays entering it from the prism (P), a clear picture of the spectrum is seen. 

 The length of the spectrum will depend upon the nature and tne number of 

 the prisms through which the light is made to pass. For ordinary purposes a 

 short spectrum is preferable for hemoglobin bands, and a spectroscope with one 

 prism is generally used. If the source of light is a lamp flame of some kina, 



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

 Institution of Washington, No. 116, 1909. 



