CHEMICAL BASIS OF THE ANIMAL BODY. 223 



thus formed results, like oxy- haemoglobin, from the union of one 

 molecule of the gas with one of haemoglobin. It further resembles 

 oxy-haemoglobin in being readily crystallisable 1 in forms isomorphous 

 with those of the former, but the crystals are on the whole less soluble, 

 brighter coloured and more stable than are those of oxy-hsemoglobin 2 . 

 They are distinctly dichromatic (see p. 217). The compound of 

 carbon-monoxide with haemoglobin is much more stable than is oxy- 

 hsemoglobin, so that the gas is not again expelled by the action of 

 oxygen, a fact which fully explains the fatal result of breathing- 

 carbon -monoxide. Finally the spectrum of carbon-monoxide haemoglobin 

 while very similar at first sight to that of oxy-haemoglobin, differs 

 distinctly from it in the position of its two absorption bands (see 

 Fig. 36, No. 6). The spectrum of this compound undergoes no change 

 by the action of any of the reducing agents described on p. 221 : this 

 affords a further characteristic means of discriminating between the 

 compounds of carbon-monoxide and oxygen with haemoglobin. Since 

 the determination of this compound in blood is frequently of considerable 

 importance in medical jurisprudence, many tests for its presence have 

 been devised additionally to the evidence afforded by the spectroscope. 

 One of the oldest and best is due to Hoppe-Seyler 3 . It consists in 

 adding to the suspected blood twice its volume of caustic soda of 

 sp. gr. 1*3. If carbon-monoxide haemoglobin is present it yields a 

 brilliant red precipitate, differing entirely in appearance from the 

 brownish green mass observed if oxy-haemoglobin is present. For 

 further tests consult the literature quoted below 4 . 



4. Nitric oxide haemoglobin. If a current of nitric oxide be 

 passed through a solution of carbon-monoxide haemoglobin, the carbon- 

 monoxide is displaced by the former gas 5 . The compound thus 

 obtained is still more stable than is carbon-monoxide haemoglobin. 

 It may be crystallised and in solution exhibits two absorption bands 

 very similar to those of oxy-haemoglobin but slightly nearer the red 

 end of the spectrum ; these bands are not affected by reducing agents. 

 If prepared by passing the gas through ordinary blood, the latter 



1 For preparation in quantity see Kiilz, Zt. f. physiol. Chem. Bd. vn. (1882), 

 S. 385. 



2 Carbon-monoxide haemoglobin is unaffected by either putrefactive changes or 

 the action of pancreatic juice. Hoppe-Seyler, Ibid. Bd. i. (1877), S. 131. 



3 Virchow's Arch. Bd. xin. (1858), S. 104. For a recent modification of this 

 test see E. Salkowski, Zt. f. physiol. Chem. Bd. xn. (1888), S. 227. 



4 Jaderholm (Swedish), Abst. in Maly's Jahresb. 1874, S. 102. Weyl u. von 

 Anrep, Arch.f. Physiol. Jahrg. 1880, S. 227. Zaleski, Zt. f. physiol. Chem. Bd. ix. 

 (1885), S. 225. Kunkel, Sitzb. d. Wiirzb. physik.-med. Gesell. 1888, Sitz. 9. 

 Katayama, Virchow's Arch. Bd. cxiv. (1889), S. 53. Welzel, Verhandl. d. physik.- 

 med. Gesell. Wiirzb. (N.F.), Bd. xxm. (1889), S. 3. 



5 L. Hermann, Arch. f. Anat. u. Physiol. Jahrg. 1865, S. 469. 



