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AN AMERICAN 7 1: XT-BOOK OF PHYSIOLOGY. 



much less easily. Methods tor preparing and purifying these crystals will be 

 found in works on Physiological Chemistry. To obtain specimens quickly 

 for examination under the microscope, one of the most certain methods is 

 to take some blood from one of the animals whose haemoglobin ervstallizes 



easily, plaee it in a test-tube, add to it a few- 

 drops of ether, shake the tube thoroughly 

 until the blood becomes laky — that is, 

 until the haemoglobin is discharged into 

 the plasma — and then place the tube 

 on ice until the crystals are deposited. 

 Small portions of the crystalline sedi- 



Cment may then be removed to a glass 

 I slide for examination. Haemoglobin 



from different animals varies not only 

 as to the ease with which it crystal- 

 lizes, but in some cases also as to the 

 form that the crystals take. In man 

 and in most of the mammalia haemoglo- 

 bin is deposited in the form of rhom- 

 bic prisms; in the guinea-pig it crys- 

 tallizes in tetrahedra (d, Fig. 1), and 

 in the squirrel in hexagonal plates. The 

 crystals are readily soluble in water, and 

 by repeated crystallizations the haemo- 

 globin may be obtained perfectly pure. 



Fig. 1. -Crystallized hemoglobin fafter Frey): ^ s j„ tne case of Other Soluble proteid- 

 a, b, crystals from venous blood of man ; r, from t . , 



the blood of a cat; d, from the blood of a like bodies, solutions of haemoglobin are 



gninea-pig; .from the blood of a hamster; /, prec ipi t ated by alcohol, by mineral acids, 

 from the blood of a squirrel. l L J » J 



by salts of the heavy metals, by boiling, 



etc. Notwithstanding the fact that haemoglobin crystallizes so readily, it is not 

 easily dialyzable, behaving in this respect like proteids and other colloidal 

 bodies. The compounds which haemoglobin forms with carbon monoxide 

 (CO) and nitric oxide (XO) are also crystallizable, the crystals being isomor- 

 phous with those of oxyhemoglobin. 



Absorption Spectra. — Solutions of haemoglobin and its derivative com- 

 pounds, when examined with a spectroscope, give distinctive absorption bands. 

 A brief account of the principle and arrangement of the spectroscope, although 

 1 1 n necessary for those familiar with the elements of Physics, is given by way 

 of introduction to the description of these 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 illus- 

 trates sufficiently well the construction of the apparatus, is shown in Figure 2, P 

 being the glass prism giving the spectrum. Light falls upon this prism through 

 the tube (a) to the left, known as the "collimator 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 



