222 CAKBOX-DIOXIDE HEMOGLOBIN. 



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. 220 : 

 this affords a further characteristic means of discriminating be- 

 tween 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. 1 It consists in adding to the sus- 

 pected 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. 2 



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. 3 The compound 

 thus obtained is still more stable than is carbon-monoxide haemo- 

 globin. 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 should first be freed from 

 oxygen by a current of hydrogen and care must be taken to 

 neutralise the nitrous acid formed during the process. 



5. Carbon-dioxide haemoglobin. The possible union of 

 carbon-dioxide with haemoglobin has already been referred to 

 (p. 221), and more recent researches have thrown further, though 

 still far from complete light upon this possibility. There appears 

 to be no doubt that a solution of haemoglobin takes up a much 

 larger volume of carbon-dioxide than can be accounted for as the 

 result of a merely physical absorption. Thus in one set of experi- 

 ments it was found * that 1 gr. of haemoglobin could unite witli 

 2-366 c.c. of the gas at a temperature of 18 4 and partial pressure 

 of 31-98 mm. of Hg, the latter being a mean average partial 

 pressure of carbon-dioxide in venous blood according to the older 



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

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



' 2 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. Knnkel, Sitzb. d. Wiirzb. physik.-med'. Gesell. 1888, Sitz. 9. 

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

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



3 L. Hermann, Arch.f. Anat. u. Physiol. Jahrg. 1865, S. 409. 



* Bohr, see Beitrdge z. Physiol. Ludwig, gewidmet, 1887, S. 164. Centralb. f. 

 Physiol. Bd. iv. (1890), S. 253. Skandinav. Arch. f. Physiol. Bd. m. Hf. 1/2 

 (1891), S. 47. See also Jolin, Arch.f. Physiol. Jahrg. 1889, Sn. 277, 285. 



