450 HAEMOGLOBIN. [Book ii. 



presence of haemoglobin. "We have already seen (§ 24) that 

 this constitutes 90 per cent, of the dried red corpuscles. There 

 can be a priori little doubt that this must be the substance with 

 which the oxygen is associated ; and to the properties of this 

 body we must therefore direct our attention. 



§ 275. Haemoglobin. When separated from the other con- 

 stituents of the serum, haemoglobin appears as a substance, 

 either amorphous or crystalline, readily soluble in water (espe- 

 cially in warm water) and in serum. 



Since haemoglobin is soluble in serum, and since the identity of 

 the crystals observed occasionally within the corpuscles with those 

 obtained in other ways shews that the haemoglobin as it exists in 

 the corpuscle is the same thing as that which is artificially prepared 

 from blood, it is evident that some peculiar relationship between 

 the stroma and the haemoglobin must, in natural blood, keep the 

 latter from being dissolved by the serum. Hence in preparing 

 haemoglobin it is necessary first of all to break up this connection 

 and to set the haemoglobin free from the corpuscles. This may be 

 done by the addition of water, of ether, of chloroform or of bile 

 salts, or by repeatedly freezing and thawing; blood so treated be- 

 comes ' laky,' cf. § 24. It is also of advantage previously to remove 

 the alkaline serum as much as possible so as to operate only on the 

 red corpuscles. The stroma and haemoglobin being thus separated, 

 a solution of haemoglobin is the result. The alkalinity of the solu- 

 tion, when present, being reduced by the cautious addition of dilute 

 acetic acid, and the solvent power of the aqueous medium being 

 diminished by the addition of one-fourth its bulk of alcohol, the 

 mixture, set aside in a temperature of 0° C. in order still further to 

 reduce the solubility of the haemoglobin, readily crystallizes, when 

 the blood used is that of the dog, cat, horse, rat, guinea-pig, &c. In 

 the case of the dog indeed it is simply sufficient to add ether care- 

 fully to the blood until it just becomes ' laky,' and then to let it 

 stand in a cool place ; the mixture soon becomes a mass of crystals. 

 The crystals may be separated by filtration, redissolved in water 

 and recrystallized. 



Haemoglobin from the blood of the rat, guinea-pig, squirrel, 

 hedgehog, horse, cat, dog, goose, and some other animals, crystal- 

 lizes readily, the crystals being generally slender four-sided 

 prisms, belonging to the rhombic system, and often appearing 

 quite acicular. The crystals from the blood of the guinea-pig 

 are octahedral, but also belong to the rhombic system ; those 

 of the squirrel are six-sided plates. The blood of the ox, 

 sheep, rabbit, pig, and man, crystallizes with difficulty. Why 

 these differences exist is not known ; but the crystals obtained 

 from different animals differ both in percentage composition 

 and in the amount of water of crystallization. In the dog, the 

 percentage composition of the crystals has been determined as 

 C. 53-85, H. 7-32, N. 16-17, O. 21-84, S. 0-39, Fe. -43, with 3 



