560 HEMOGLOBIN. [BOOK n. 



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 becomes '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 solution, 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 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 carefully 

 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 nitration, redissolved in water and re- 

 crystallized. 



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 composition and the amount of water 

 of crystallization vary somewhat in the crystals obtained from 

 different animals. In the dog, the percentage composition of the 

 crystals has been determined as C. 53'85, H. 7'32, N. 1617, 

 0. 21-84, S. 0'39, Fe. '43, with 3 to 4 per cent, of water of crystal- 

 lization. It will thus be seen that haemoglobin contains, in 

 addition to the other elements usually present in proteid sub- 

 stances, a certain amount of iron ; that is to say, the element iron 

 is a distinct part of the haemoglobin molecule : a fact which of 

 itself renders haemoglobin remarkable among the chemical sub- 

 stances present in the animal body. 



345. The crystals, when seen in a sufficiently thick layer 

 under the microscope, have the same bright scarlet colour as 

 arterial blood has to the naked eye ; when seen in a mass they 

 naturally appear darker. An aqueous solution of haemoglobin, 

 obtained by dissolving purified crystals in distilled water, has also 



