218 OXY-HAEMOGLOBIN. 



same statement therefore probably holds good for haemoglobin. When 

 decomposed in the absence of oxygen (air), as for instance by the 

 action of organic acids, more dilute mineral acids or best of all by 

 caustic alkalis, it yields a proteid, of which but little is known (see p. 

 31), and a coloured substance called by Hoppe-Seyler haemochromogen. 

 The latter on exposure to air absorbs oxygen and becomes ordinary 

 haematin ; it is in fact the substance usually spoken of as reduced 

 haematin. (See below.) 



2. Oxy-hsemoglobin. When haemoglobin is exposed to the 

 air it rapidly unites, molecule for molecule, with oxygen thus becoming 

 oxy-haemoglobin, the characteristic constituent of the red-corpuscles to 

 which the scarlet colour of arterial blood is due 1 . It may be readily 

 set free from the corpuscles by the addition to defibrinated blood of 

 such fluids as alcohol, ether, chloroform, water and solutions of bile- 

 salts or by repeatedly freezing and thawing the blood ; when thus 

 set free it passes into solution in the adjacent serum. From this 

 solution it may be obtained as crystals with more or less readiness, 

 dependently upon the kind of animal whose blood is used for its 

 preparation (see 344), the difference being due partly at least to 

 the varying solubility of the several haemoglobins. 



To obtain rapidly a microscopic preparation of oxy-haemoglobin 

 crystals it suffices to take a drop of the blood of some animal whose 

 haemoglobin crystallises readily (rat, guinea-pig or dog), to mix a drop 

 of it on a slide with a minute drop of water and allow the mixture 

 to evaporate until a ring of dried substance is formed at the peri- 

 phery. If it be now covered with a cover-slip, crystals usually form 

 in a short time, especially if it be kept cooled. For the preparation 

 of oxy-haemoglobin crystals on a large scale many methods, the same in 

 general principles but differing somewhat in detail, have been proposed, 

 the difficulty of the preparation varying considerably according to the 

 kind of blood used 2 . For laboratory purposes large quantities of 

 crystallised oxy-haemoglobin may be very readily obtained from dog's 

 blood as follows (Kiihne). The blood is defibrinated and strained 

 through fine muslin ; it is then placed in a flask and ether is added 

 with frequent shaking until the blood is just 'laky,' i.e. transparent. 

 The flask is now surrounded by a freezing mixture of ice and salt and 



1 Haemoglobin is united to corpuscles in the blood of all vertebrates with two 

 exceptions. In invertebrate blood it is usually found in solution in the plasma, 

 but there are a few (eight) exceptions to this rule. For details and literature see 

 Halliburton, Chem. Physiol. and PathoL 1891, pp. 267, 316. 



2 For fuller details see Gamgee, Physiol. Chemistry, Vol. i. 1880, p. 85. See 

 later Otto, Zt. f. physiol Chem. Bd. vn. (1882), S. 57. Zinoffsky, Ibid. Bd. x. 

 (1885), S. 18. Hiifner, Beitr. z. Physiol. Festschr. f. C. Ludivig, 1887, S. 74. 

 Mayet, Compt. Rend. T. 109 (1890), p. 156. 



