88 The Functions of the Blood. 



posed by a prism, two dark bands make their appearance in 

 the green portion of the spectrum. Stokes repeated and 

 verified the fact, and it soon became in his hands the starting- 

 point of a new train of research. 



He treated a solution of blood-corpuscles with an alkaline 

 reducing agent, and observed that its colour almost instantly- 

 changed from scarlet to purple-red, the hue of veinous blood. 

 On examining the spectrum, he now found that the two dark 

 lines had disappeared, and that a single line, intermediate in 

 position between them, had become visible. On shaking the 

 tube with air, the scarlet colour and the two lines at once re- 

 turned, but, after a few minutes, again disappeared ; and this 

 could be repeated many times. Hence it was evident that the 

 scarlet arterial blood lost its oxygen to the reducing agent, 

 and subsequently recovered it again, when shaken, from the 

 air. The fact is so important that I prefer to give it in Stokes's 

 own words. He says, — 



" The colouring matter of blood, like indigo, is capable of 

 existing in two states of oxidation, distinguishable by a 

 difference of colour, and a fundamental difference in the action 

 on the spectrum. It may be made to pass from the more to 

 the less oxidized state, by the action of suitable reducing 

 agents, and recovers its oxygen by absorption from the 

 air."* 



Hoppe-Seyler had shown that this colouring matter is 

 different from the so-called hc&matin, which is obtainable by 

 artificial means from the blood, and Dr. Sharpey therefore 

 suggested that the true colouring matter should be named 

 cruorine. The name is a good one, and does not, like 

 " hasmato-globulin," which is adopted by Hoppe-Seyler, in- 

 volve any hypothesis. In the oxidized — the scarlet state — it 

 is distinguished as scarlet cruorine, and in the reduced state as 

 purple cruorine. It is hardly necessary to point out how in- 

 telligible an explanation these facts afford of the oxygen- 

 carrying power of the blood-corpuscles. In the lungs the 

 purple cruorine of veinous blood takes up oxygen, and becomes 

 scarlet cruorine ; and in the whole of the general circulation, 

 but more particularly in the capillaries, oxidation is effected by 

 means of this oxygen, and the cruorine, to a great extent, 

 passes back to the purple state. Hoppe-Seyler has since 

 found that the blood of a rabbit which has been killed by 

 drowning exhibits the spectrum of purple cruorine. In or- 

 dinary states, however, even veinous blood retains enough 

 unreduced cruorine to give the two-line spectrum. 



But Stokes has discovered another fact which is of extreme 

 importance in regard to the question of animal oxidation. He 



* " Proceedings of the Royal Society," vol. xiii. 357. 



