COLORING MATTERS. 95 



These characters form a very delicate test for the coloring matter of 

 blood. Prever has found that with a solution of pure hemoglobine in 

 water, of 4 parts per ten thousand, the absorption bands may still be 

 seen, though the second one is very faint ; and according to Hoppe- 

 Seyler, a solution of one part in ten thousand will allow them to be 

 recognized if viewed in a layer one centimetre in thickness. Fresh 

 dog's blood, if diluted with 1,000 parts of water, and viewed in a layer 

 of 3 centimetres' thickness, will show a spectrum in which both absorp- 

 tion bands are distinctly perceptible though not very strong. If diluted 

 with 10,000 parts of water, and viewed in a layer of 4.5 centimetres, 

 the first band is still visible, though very faint ; the second is imper- 

 ceptible. 



The condition of hemoglobine, in regard to its absorption of oxygen, 

 has a marked effect on its spectroscopic characters. The spectrum 

 with two absorption bands, above described, is that of hemoglobine 

 which has absorbed all the oxygen which it is capable of holding in 

 loose combination. If this oxygen be removed, the color of the 

 solution is modified and its spectrum changes. The coloring matter 

 is no longer oxyhemoglobine, but has become reduced hemoglobine ; 

 and its spectrum, instead of two absorption bands, shows but one, 

 comparatively wide and ill-defined, the darkest part of which occupies 



FIG. 13. 



T. Spectrum of Oxyhemoglobine. 



II. Spectrum of Reduced Hemoglobine. 



exactly the space formerly intervening between the two. At the same 

 time the dim borders of the obscured portion shift toward the left ; so 

 that the orange in the neighborhood of the line D is less brilliant than 

 before, while nearly the whole of the green becomes visible to the left 

 of the line E. The blue is also extended a little toward the right. 

 (Fig. 13, II.) 



The coloring matter of the blood may be deprived of its loosely 

 combined oxygen by evacuation with the air-pump, treatment with a 

 current of hydrogen or nitrogen, the addition of deoxidizing agents, or 



