AFFINITY OF CRUORIN FOR OXYGEN. 831 



which it differs in color and in its action on the spectrum. The hse- 

 matin of Lecanu is an artificial compound, produced bj the decompo- 

 sition of this cruorin by powerful acids, and is named by Stokes brown 

 hcematin, to distinguish it from red hcematin, formed by the oxidation 

 of the brown variety, both of which show different absorption bands 

 to those of cruorin. 



The cruorin in its bright condition, is named scarlet cruorin, and in 

 its dark condition, purple cruorin ; the former gives the spectrum with 

 two dark bands and an intermediate light one, and the latter, that with 

 a single dark band. The purple cruorin, or deoxygenated kind, is 

 supposed to exist in venous blood, and the scarlet, or oxygenated kind, 

 in arterial blood. The evident attraction of cruorin for oxygen, is 

 supposed to account for the absorption and combination of that gas 

 with the blood ; and thus, also, for the special attraction or affinity of 

 the red corpuscles for oxygen, of which, indeed, they have been often 

 named the carriers. 



As apparently opposed to these conclusions, it is found that ordinary 

 venous blood exhibits the spectrum of the scarlet cruorin, and not that 

 of the purple cruorin ; but this, as observed by Stokes, may merely 

 show that most of the cruorin in venous blood is still scarlet cruorin, 

 the coloring substance being only partially converted into the purple 

 condition. Venous blood, indeed, like arterial blood, still contains 

 oxygen, as well as carbonic acid, though in different proportions ; and, 

 although it is unequal to the perfect maintenance of the functions of 

 the muscular and nervous substance, it is still better than no blood at 

 all. (Brown-Sequard.) Moreover, extensive hemorrhage is not neces- 

 sarily fatal ; and persons affected with chlorosis exhale carbonic acid 

 as freely as those in health. It is possible, also, that carbonic acid 

 may act less powerfully when the blood is undiluted, than when, as in 

 experiments, it is mixed with water. 



The cruorin of the blood being supposed, in the act of respiration, 

 to undergo oxygenation as it assumes its scarlet color, its deoxygena- 

 tion or reduction may be effected by substances contained in the 

 blood, which themselves undergo oxidation at its expense. Such a 

 change certainly takes place in blood diluted and put aside before pu- 

 trefaction takes place, the spectrum being distinctly altered to that of 

 purple cruorin, and being changed back again to that of scarlet cru- 

 orin, by agitation with air. A temperature as high as that of the 

 blood in the body facilitates these changes. 



The possible mode of occurrence of such alternate changes in the blood in 

 the systemic and the pulmonary capillaries, is illustrated by Stokes, by first re- 

 ducing or deoxygenating, a solution of scarlet cruorin, by means of a slightly 

 alkaline solution of the protoxide of tin in tartaric acid, and then reoxygena- 

 ting it, by agitation of the altered colored solution with air. If the mixture 

 be now allowed to stand for two or three minutes, the coloring matter is again 

 slowly deoxidized ; by agitation it is once more oxidized ; and so on for a number 

 of times. In this experiment, the purple cruorin, absorbs oxygen more readily 

 than the salt of tin does ; but afterwards, it slowly parts with oxygen to that 

 salt. 



In the same way, the purple cruorin, as it passes through the lungs, 

 absorbs oxygen by a special affinity, and then in circulating through the 



