COLOUR OF REDUCED HEMOGLOBIN. 



233 



When the blood crystals of horses' blood are prepared in closed 

 vessels, it happens very frequently that large quantities of hexagonal 

 tables of a dark red colour are found mixed with the well-known ordinary 

 prisms. If a drop of the liquid in which the crystals are suspended be 

 examined with the microscope, without a cover-glass, the hexagonal plates 

 are observed rapidly to liquefy, and simultaneously bundles of fine, 

 bright-red prismatic needles appear. Nencki long ago showed that the 

 dark red hexagonal tables are crystals of reduced haemoglobin, whilst 

 the scarlet prisms are those of oxyhaemoglobin. Horses' blood appears 

 peculiarly apt to give crystals of the reduced blood-colouring matter. 

 In the preparation of the haemoglobin of the horses' blood by ordinary 

 methods, i.e. without special precautions in reference to the access of 

 air, both forms of crystals are usually obtained. 1 



THE ABSORPTION OF LIGHT BY SOLUTIONS OF EEDUCED HEMOGLOBIN. 



Colour of solutions : dichroism. In thick layers, or in thin layers 

 if concentrated, solutions of reduced haemoglobin present a dark cherry- 

 red colour, whilst very dilute solutions exhibit a green tint. 



H.-EMOGLOBIN. 



ABC 



FIG. 34. Graphic representation of the spectrum of (] ) oxyheemoglobin 

 and (2) haemoglobin. The numbers at the right-hand side of each 

 diagram indicate percentages. After Rollett. 



This dichroism is also characteristic of the blood of asphyxiated 

 animals, and was first observed by Brticke. It is specially to be noted 

 that, whilst solutions of reduced haemoglobin are dichroic, solutions of the 

 2 - CO- and NQ-compounds of haemoglobin exhibit no trace of dichroism. 



Cause of the differences observed in the colour of blood contrasted 

 with that of solutions of haemoglobin. The much brighter colour pre- 

 sented by blood, as contrasted with corresponding solutions of the blood- 

 colouring matter, depends upon the presence of the blood corpuscles. 

 Were we to conceive, as Eollett argues, the blood corpuscles suspended 

 in the liquor sanguinis or in serum, and retaining all their physical 

 properties save their colour, then, as a result of the repeated total reflec- 

 tions, due to the differences in the refractive indices of the corpuscles 

 and the fluid in which they float, blood would appear as white as milk. 



1 Hiifner, op. cit., Arch. f. PhysioL, Leipzig, 1894, S. 150. 



