830 SPECIAL PHYSIOLOGY. 



which to magnify the spectrum. This method is the so-called spectrum analysis, 

 by which, not only have new substances been detected in chemical processes 

 upon the earth, but some at least of the constituents of the luminous atmos- 

 pheres of distant stars have been determined. It has also been employed to 

 follow the entrance of peculiar substances, such as lithium and caesium, into 

 the blood and tissues of living animals, to measure their rate of absorption, 

 their preference for particular tissues, and their periods of excretion from the 

 body. (Bence Jones.) To the same observer we owe very interesting re- 

 searches, in which the fluorescent property of quinine (p. 431) is made use of, 

 to follow that substance into, and out of, the living economy, by its presence 

 or absence in the crystalline lens of the eye. It, moreover, appears that a 

 peculiar animal substance, also fluorescent, and therefore named by Dr. Jones, 

 quinoidin, is constantly present in the animal body. 



Amongst other results of the spectrum analysis of colored solutions, it was 

 discovered by Hoppe, that dilute solutions of blood produce two peculiar dark 

 absorption bands of great beauty and distinctness, situated in the spectrum, 

 between the D and E lines of Frauenhofer, and having a remarkably bright 

 intermediate color band. He showed that this spectrum was formed by the 

 colored blood of animals generally ; that the red coloring substance seemed to 

 remain unchanged by the action of alkaline carbonates and caustic ammonia, 

 for its spectrum remained unaltered ; but that it was instantly decomposed by 

 acids, and more slowly by caustic alkalies, a substance being then producecl, 

 which causes different absorption bands, and corresponds with the hsematin of 

 Lecanu. 



This subject has since been further investigated by Professor Stokes. To 

 examine the natural blood spectrum, he placed a small portion of blood well 

 diluted with water, or a watery extract of the clot, in a test-tube ; this being 

 held up to the light, behind a fine slit in a piece of black card or a metal plate, 

 and looked at through a prism, the two characteristic, sharply-defined, dark 

 absorption bands, with the intermediate bright streak, were readily seen. On 

 adding to the colored solution a reagent capable of abstracting oxygen from it, 

 a remarkable change occurred in the spectrum. First, it became a little 

 darker ; but, besides this, instead of the two dark bands with their intermedi- 

 ate bright streak, a single, broader, and less defined band was now seen, situ- 

 ated nearly opposite the place of the bright band in the spectrum of the simple 

 solution. Since the solution of blood is alkaline, and since acids, as just men- 

 tioned, decompose its coloring substance, it was necessary to employ a pecu- 

 liar deoxygenating agent ; the one selected was a solution of protosulphate of 

 iron, containing a small quantity of tartaric acid, which prevents the precipi- 

 tation of the iron by alkalies ; this was rendered slightly alkaline by a little 

 soda. On next exposing the deoxygenated and altered colored solution to the 

 air in a shallow vessel, or on agitating it with air, by shaking it in a long 

 tube, it was found that the color again became brighter, and that, on examina- 

 tion with the prism, the characteristic dark bands, with the intermediate bright 

 one, again appeared. These changes were evidently attributable to the reoxy- 

 genation of the coloring substance by the oxygen of the air. This beautiful 

 experiment realized the supposition previously entertained by Stokes, that he 

 might imitate, and possibly explain, the change of color of arterial into ve- 

 nous, and of venous into arterial blood. That the single band of the altered 

 solution does not belong to the reagent, is shown by examining that separately ; 

 and that it is not produced by a compound of the reagent with the coloring 

 substance, but simply by deoxygenation of the latter, is proved by the same 

 effects being produced by other deoxidizing agents, such as protochloride of 

 tin, and hydrosulphuret of ammonia, and also by the ordinary and well- 

 known displacement of oxygen, by means of carbonic acid. Moreover, these 

 reagents have themselves no power to produce the newly-observed color band. 



From these experiments, it is concluded by Stokes, that there exists 

 in the blood a natural coloring matter, which might be named cruorin, 

 capable, like the coloring matter of indigo, of assuming, by alternate 

 abstraction and reintroduction of oxygen, two states of oxidation, in 



