CHAP, ii.] RESPIRATION. 335 



In each oi' the six cases the layer brought before the spectroscope was 1 c.m. in 

 thickness. 



The Letters (A, a &c.) indicate Frauenhofer's lines, and the figures wave-lengths 

 expressed in 100,000th of a millimetre. 



all to break up 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. 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 corpuscles being thus broken up, a solution of haemoglobin is 

 the result. The alkalinity of the solution, when present, being re- 

 duced 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 haemo- 

 globin, 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 to the blood 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 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 octa- 

 hedral, 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 is, according to Hoppe-Seyler, C. 53'85, H. 7'32, N. 1617, 

 O. 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 hemoglobin molecule: a fact which of 

 itself renders haemoglobin remarkable among the chemical sub- 

 stances present in the animal body. 



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 dis- 

 solving purified crystals in distilled water, has also the same 

 bright arterial colour. A tolerably dilute solution placed before 

 tne spectroscope is found to absorb certain rays of light in a 

 peculiar and characteristic manner. A portion of the red end of 

 the spectrum is absorbed, as is also a much larger portion of the 

 blue end ; but what is most striking is the presence of two 



