197 



removed from blackness than earbon. The disap- 

 pearance of the black colour of the blood, as carbo- 

 nic acid is formed in respiration, is no proof of such 

 blood losing its colour, in consequence of yielding 

 carbon ; for we have seen, that, by living vegetables, 

 by animals, and by the human skin itself, this acid 

 is equally formed where no black blood is present 

 to supply carbon. Dr Lower also relates the case 

 of a young woman bled in the foot, whose blood 

 was as white as milk, and yet she was in good health : 

 and, in two other cases, the blood drawn from a 

 vein in the arm, was of the same complexion *. The 

 loss of the black colour of the blood too may be 

 owing to the acquisition, rather than to' the escape, 

 of some colouring matter ; or it may arise from 

 some change in the properties of the blood, which 

 shall vary its power of reflecting the rays of light. 

 Neither because carbonic acid is formed by exposing 

 black blood to the air, can we admit this as a proof, 

 that its blackness arose from the presence of car- 

 bon ; for Dr Girtanner found, that this acid was 

 formed equally by arterial blood (101.), which is 

 red : and we have seen it to be produced by the se- 

 rum (97.)? as we ^ as by the crassamentum of the 

 blood. Other agents also, which are totally inde- 

 pendent of carbon, are capable of producing this 

 black colour in the blood. Every one knows, that 

 a part exposed to great cold, speedily becomes black : 

 and Dr Crawford found, that, on immersing a dog, 

 whose temperature was 100, in water at 45, the 



* Lowthorpe's Abrid. Phil. Trans, vol. iii. p. 239, 



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