362 Prof. Stokes on the Reduction and Oxidation [June 16, 



otherwise, any extensive hsemorrhage could hardly fail to be fatal, if, as 

 there is reason to believe, cruorine be the substance on which the function 

 of respiration mainly depends ; nor could chlorotic persons exhale as much 

 carbonic acid as healthy subjects, as is found to be the case. 



But after death there is every reason to think that the process of reduc- 

 tion still goes on, especially in the case of warm-blooded animals, while 

 the body is still warm. Hence the blood found in the veins of an animal 

 some time after death can hardly be taken as a fair specimen as to colour 

 of the venous blood in the living animal. Moreover the blood of an animal 

 which has been subjected to abnormal conditions before death is of course 

 liable to be altered thereby. The terms in which Lehmann has described 

 the colour of the blood of frogs which had been slowly asphyxiated by 

 being made to breathe a mixture of air and carbonic acid seem unmistake- 

 ably to point to purple cruorine*. 



18. The effect of various indifferent reagents in changing the colour of 

 defibrinated blood has been much studied, but not always with due regard 

 to optical principles. The brightening of the colour, as seen by reflexion, 

 produced by the first action of neutral salts, and the darkening caused by 

 the addition of a little water, are, I conceive, easily explained ; but I have 

 not seen stated what I feel satisfied is the true explanation. In the former 

 case the corpuscles lose water by exosmose, and become thereby more 

 highly refractive, in consequence of which a more copious reflexion takes 

 place at the common surface of the corpuscles and the surrounding fluid. 

 In the latter case they gain water by endosmose, which makes their refrac- 

 tive power more nearly equal to that of the fluid in which they are con- 

 tained, and the reflexion is consequently diminished. There is nothing in 

 these cases to indicate any change in the mode in which light is absorbed 

 by the colouring matter, although a change of tint to a certain extent, and 

 not merely a change of intensity, may accompany the change of conditions 

 under which the turbid mixture is seen, as I have elsewhere more fully 

 explained!. 



No doubt the form of the corpuscles is changed by the action of the 

 reagents introduced ; but to attribute the change of colour to this is, I ap- 

 prehend, to mistake a concomitant for a cause, and to attribute, moreover, 

 the change of colour to a cause inadequate to produce it. 



19. Very different is the effect of carbonic acid. In this case the ex- 

 istence of a fundamental change in the mode of absorption cannot be ques- 

 tioned, especially when the fluid is squeezed thin between two glasses and 

 viewed by transmitted light. I took two portions of defibrinated blood ; to 

 one I added a little of the reducing iron solution, and passed carbonic acid 

 into the other, and then compared them. They were as nearly as possible 

 alike. We must not attribute these apparently identical changes to two 

 totally different causes if one will suflSce. Now in the case of the iron 



* Physiological Chemistry, vol. ii. p. 178. 

 t Philosophical Transactions, 1852, p, 527. 



