CHEMICAL BASIS OF THE ANIMAL BODY. 221 



have been made 1 , but these while they tell us at most that it consists 

 of oxygen, hydrogen, nitrogen, and carbon together with iron as a 

 characteristic constituent and some sulphur, and seem to indicate that 

 it differs in composition as obtained from different animals, do not as 

 yet enable us to assign with any certainty a definite formula to its 

 composition. It is however certain that its molecular weight is enor- 

 mously great (13000 UOOO) 2 . 



The spectroscopic appearances of solutions of oxy-haemoglobin have 

 been already sufficiently described and figured ( 345). (For convenience 

 of reference Fig. 75 is reproduced here.) When its solutions are heated 

 or it is treated either in solution or as a solid with acids or alkalis, it 

 may be readily decomposed, yielding a proteid as in the case of haemo- 

 globin and a coloured residue, viz. haematin. (See below.) The oxygen 

 which is loosely combined with haemoglobin in the formation of oxy- 

 haemoglobin may be readily removed by several means of which the 

 following are those most usually employed. 



(i) The solution is warmed to 40 and the gas driven off by exposure 

 to the vacuum of a mercurial pump, (ii) A current of some neutral gas 

 such as hydrogen or nitrogen is passed through the solution, (iii) The 

 solution is treated with a few drops of some reducing agent such as 

 Stokes' fluid 3 . This is prepared by adding tartaric or citric acid to a 

 solution of ferrous sulphate and then ammonia until it is strongly 

 alkaline. This reagent does not keep and must be freshly prepared 

 each time it is required. Instead of Stokes' fluid, ammonium sulphide 

 may be used, but in this case some slight manipulation is frequently 

 required to ensure reduction. A few drops of the sulphide are added 

 to the solution which is then gently warmed : if on examination with 

 the spectroscope it is found that the reduction has not taken place, as 

 shown by the persistence of the two bands of oxy-hsemoglobin, a little 

 more of the sulphide may be added and the mixture again carefully 

 warmed. 



The amount of oxygen, removable by the means just described, 

 with which one gram of haemoglobin (from dog's blood) can unite is 

 usually stated as being 1*59 c.c. at and 760 mm. Hg. this constant 

 being taken as independent of the concentration of the solutions 

 employed 4 . Quite recently some doubt has been cast on the quantity 

 being thus constant ; and it has been stated that several modifica- 



1 See Hammarsten's Lehrb. d. physiol. Chem. 1891, S. 57 ; or Halliburton's 

 Text-book of Chem. Physiol. Pathol. 1891, p. 286. 



' 2 Marshall, Zt. f. physiol. Chem. Bd. vn. (1882), S. 81. Kiilz, Ibid. S. 384. 

 Cf. Zinoffsky, Ibid. Bd. x. (1886), S. 16, and see Hiifner, loc. cit. 



3 Proc. Roy. Soc. June, 1864. Phil. Mag. November, 1864. 



4 Hiifner, Zt. f. physiol. Chem. Bd. i. (1878), Sn. 317, 386. See also Jn. f. 

 prakt. Chem. Bd. xxn. (1880), S. 362. 



