OX YH/EMO GL OBJ. V. 193 
distinguish it from reduced haemoglobin! The only distinction which Hoppe- 
Seyler found to exist between "arterin " and " pblebin " consisted in the alleged 
greater ease with which tlie hypothetical constituent of arterial blood yielded 
its dissociable oxygen, when boiled in vacuo, as compared with the hypo- 
thetical constituent of venous blood. To establish this alleged difference 
between arterial and venous blood would require a body of experimental facts, 
such as does not exist. Even were the difference shown to be a real one, it 
would in no way support the hypothesis of a radical difference between the 
colouring matter of arterial and venous blood. But the investigations of 
Hiifner, which have proved with mathematical accuracy that the colouring 
matter of the blood behaves, both in so far as its optical characters and 
its relations to oxygen are concerned, precisely as a solution of haemoglobin, 
and is the only coloured constituent of the corpuscles, complete the demonstra- 
tion of the erroneous nature of the hypothesis advanced by Hoppe-Seyler 
on this subject. 
OXYHEMOGLOBIN. 
Methods of Preparation. 
Introductory remarks. — It has already been stated that the blood- 
colouring matter of different species of animals is not, in all particulars, 
absolutely identical. Although behaving in the same manner in refer- 
ence to the gases with which it can combine to form more or less 
easily dissociated compounds, and whilst possessing identical powers of 
absorbing the rays of the spectrum, the haemoglobin of different animals 
exhibits differences (1) in crystalline form, (2) in solubility, (3) in the 
quantity of water of crystallisation, (4) in percentage composition. 
These differences will be carefully examined in the sequel, but attention 
is drawn to them in this place, in relation to another point of difference, 
namely, the variation in the facility of separating haemoglobin in a 
crystalline form. From the blood of certain animals, crystals of haemo- 
globin can most readily be prepared, whilst in other cases the task 
is one of very considerable difficulty. Among the conditions which 
influence the result, the degree of solubility of the blood-colouring 
matter is the chief. Thus the blood of the rat, the guinea-pig, and 
the squirrel, which contains the least soluble haemoglobin, yields crystals 
with great facility ; whilst the blood of man, and that of the domestic 
herbivorous animals, which possess haemoglobin of remarkable solu- 
bility, yields crystals with extraordinary difficulty. It is impossible 
to state with accuracy the relative facility of crystallisation of the 
haemoglobin of different animals, but the following statements are pro- 
bably correct. The blood of the rat, the guinea-pig, and the squirrel 
crystallises most readily: next comes the blood of the cat, the dog, and 
the horse : the blood of man and the pig follow-, whilst that of the 
rabbit, the sheep, the ox, and the frog crystallise with the greatest 
difficulty. 
The principle upon which the majority of the methods for the 
separation of haemoglobin in a crystalline form are based is the 
following:: — To effect the solution of the haemoglobin of the coloured 
corpuscles in the serum, or in water, added to the previously separated 
corpuscles : and thereafter, by the addition of alcohol, or of ether, or 
by the agency of cold, or of both cold and alcohol or ether conjointly, 
sometimes aided by the process of evaporation, to cause the haemoglobin, 
vol. 1. — 17. 
