OXYH^EMOGLOBIN. 193 



distinguish it from reduced haemoglobin ! The only distinction which Hoppe- 

 Seyler found to exist between " arterin " and " phlebin " consisted in the alleged 

 greater ease with which the 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. 



OXYELEMOGLOBIN. 



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. i. 13 



