Prof. Stokes on the Colouring Matte?' of the Blood. 397 



14. Hoppe proposed to employ the highly characteristic absorp- 

 tion-bands of scarlet cruorine in forensic inquiries. Since, however, 

 cruorine is very easily decomposed, as by hot water, alcohol, weak 

 acids, &c, the method would often be inapplicable. But as in such 

 cases the coloured product of decomposition is hsematine, which is a 

 very stable substance, the absorption-bands of red hsematine in alka- 

 line solution, which in sharpness, distinctive character and sensibi- 

 lity rival those of scarlet cruorine itself, may be employed instead 

 of the latter. The absorption-bands of brown hsematine dissolved 

 in a mixture of ether and acetic acid, or in acetic acid alone, are 

 hardly less characteristic, but are not quite so sensitive, requiring a 

 somewhat larger quantity of the substance. 



15. I have purposely abstained from physiological speculations 

 until I should have finished the chemico-optical part of the sub- 

 ject ; but as the facts which have been adduced seem calculated to 

 throw considerable light on the function of cruorine in the animal 

 economy, I may perhaps be permitted to make a few remarks on 

 this subject. 



It has been a disputed point whether the oxygen introduced into 

 the blood in its passage through the lungs is simply dissolved or is 

 chemically combined with some constituent of the blood. The latter 

 and more natural view seems for a time to have given place to the for- 

 mer in consequence of the experiments of Magnus. But Liebig and 

 others have since adduced arguments to show that the oxygen 

 absorbed is, mainly at least, chemically combined, be it only in such 

 a loose way, like a portion of the carbonic acid in bicarbonate of soda, 

 that it is capable of being expelled by indifferent gases. It is known, 

 too, that it is the red corpuscles in which the faculty of absorbing 

 oxygen mainly resides. 



Now it has been shown in this paper that we have in cruorine a 

 substance capable of undergoing reduction and oxidation, more espe- 

 cially oxidation, so that if we may assume the presence of purple 

 cruorine in venous blood, we have all that is necessary to account 

 for the absorption and chemical combination of the inspired oxygen. 



16. It is stated by Hoppe that venous as well as arterial blood 

 shows the two bands which are characteristic of what has been called 

 in this paper scarlet cruorine. As the precautions taken to prevent 

 the absorption of oxygen are not mentioned, it seemed desirable to 

 repeat the experiment, which Dr. Harley and Dr. Sharpey have 

 kindly doue. A pipette adapted to a syringe was filled with water 

 which had been boiled and cooled without exposure to the air, and 

 the point having been introduced into the jugular vein of a live dog, 

 a little blood was drawn into the bulb. Without the water the 

 blood would have been too dark for spectral analysis. The colour 

 did not much differ from that of scarlet cruorine ; certainly it was 

 much nearer the scarlet than the purple substance. The spectrum 

 showed the bands of scarlet cruorine. 



This, however, does not by any means prove the absence of purple 

 cruorine, but only shows that the colouring matter present was 

 chiefly scarlet cruorine. Indeed the relative proportions of the two 

 present in a mixture of them with one another and with colourless 



