250 THE BLOOD. 



no marked difference, either of color or of spectroscopic characters, is 

 to be seen between the blood in the arteries and capillaries, and that in 

 the veins. But if by any means the blood or a solution of hemoglobine 

 be deprived of its oxygen, and examined in that condition, it at once 

 shows a decided change both in color and spectroscopic appearances. 



This reduction or deoxidation of the coloring matter of the blood may 

 be effected in either of two ways, namely, first, by the addition of deoxi- 

 dizing agents, and secondly by keeping the blood for a time excluded 

 from the access of air. According to the experiments of Stokes, the 

 addition of iron protosulphate to fresh blood reduces the hemoglobine, 

 and changes its color from bright red to dark purple ; the scarlet color 

 being again restored by agitating the blood with oxygen or atmospheric 

 air. Other observers have accomplished the reduction of the hemoglo- 

 bine by continued treatment of the blood or its solutions with a stream 

 of carbonic acid. The second method, however, is more easily applied. 

 If a solution of fresh blood, of a bright scarlet color, which yields a 

 spectrum with the absorption bands of aerated hemoglobine fully devel- 

 oped, be inclosed in a securely stoppered test-tube, the whole of which 

 it completely fills, and be kept in this condition secluded from the air 

 for twenty-four or forty-eight hours, the hemoglobine at the end of that 

 time will have lost its oxygen which has entered into other combinations. 

 If now placed before the spectroscope, the solution will show a spectrum 

 in which the two absorption bands above described have disappeared, 

 and which shows in place of them a single wide and comparatively ill- 

 defined band covering about three-quarters of the distance from D to E, 

 and extending usually toward the red a little beyond the situation of 

 the line I). The darkest part of this absorption band occupies exactly 

 the space which intervened between the two former bands. 



Fig. 83. 



SPECTRUM OF REDUCED HEMOGLOBIXE. 



If the solution be now shaken up for a few instants with atmospheric 

 air. its bright color is at once restored, and at the same time the single 

 absorption band of reduced hemoglobine disappears, and is replaced by 

 the two normal bands of oxidized or aerated blood. These changes 

 may be repeated until the blood begins to show the effect of putrefaction. 



Red Globules of the Blood in different Classes of Animals. In all 

 vertebrate animals the blood contains red globules, of which the color- 



