COLOUR OF REDUCED HAEMOGLOBIN. 
233 
When the bl I crystals of horses 5 blood are prepared in closed 
vessels, it happens very frequently that large quantities of hexagonal 
tables of a dark n d 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 tine, 
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 oxyhemoglobin. 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 Reduced Haemoglobin. 
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. 
Oxyhemoglobin. 
HAEMOGLOBIN. 
ABC 
Fig. 
34. — Graphic representation of the spectrum of — (1) oxyhemoglobin 
and (2) hremoglobin. 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 Briicke. It is specially to be noted 
that, whilst solutions of reduced haemoglobin arc dichroie, solutions of the 
2 - CO- and NO -compounds of hmmoglobin exhibit no trace of dichroism. 
Cause of the differences observed in the colour of blood contrasted 
with that of solutions of hmmoglobin. — 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 Rollett 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 w T ould appear as white as milk. 
1 Hufner, op. cit., Arch. f. Physiol., Leipzig, 1894, S. 150. 
