CHAP. II.] THE BLOOD. 107 



therefore in investigating whether NO can form a compound with 

 haemoglobin, analogous to the oxygen and carbonic oxide compounds, 

 certain precautions had to be taken; for firstly, by combining with the 

 respiratory O of haemoglobin, NO ? would be formed, and next, by the 

 reaction of water upon this body, nitric acid would result, which would 

 immediately decompose the haemoglobin. 



Hermann added ammonia to blood and then passed a stream of 

 NO through it; all the acid generated in the reaction, at the expense 

 of the oxygen of haemoglobin, was neutralised by the ammonia, and 

 thereafter a compound of NO with haemoglobin was formed. 



Again when CO-haemoglobin was placed in a vessel from which 

 the air had been expelled and then a stream of NO was passed 

 through the liquid, this gas displaced the CO, and combined with the 

 haemoglobin in its stead. 



Hermann found that the body thus produced yielded crystals 

 isomorphous with those of the oxygen and carbonic oxide compounds, 

 and that its spectrum presented a spectrum closely resembling theirs, 

 though like that of the CO-haemoglobin undergoing no change after 

 the addition of reducing agents. 



We are therefore acquainted with three compounds of haemo- 

 globin with gases which are isomorphous, and in which presumably 1 

 molecule of haemoglobin is linked with 1 molecule of the gas. The 

 least stable of these compounds is that with oxygen, for it can be 

 decomposed by CO, which then takes its place, forming a compound 

 of intermediate stability, which in its turn can be decomposed 

 by NO. That in each case a molecule of the gas takes part in the 

 reaction is argued from the facts that CO displaces an equal 

 volume of (O 2 occupying the same volume as CO) and that the 

 three compounds are isomorphous, so that the constitution of the NO- 

 compound will almost certainly be similar to that of the CO body 1 . 

 Acetylene, In the case of both CO and NO we have unsaturated bodies 



C 2 H 2- which presumably satisfy their free affinities by linking them- 



selves to the complex molecule of haemoglobin, and it is quite conceivable 

 that other similarly constituted bodies might exert a similar action. It has 

 indeed been surmised 2 that Acetylene or Ethine, C 2 H 2 , actually does so form 

 a very unstable compound with haemoglobin, easily reducible by ammonium 

 sulphide or reducing tin solutions. An investigation made with a view 

 of testing the results in Hermann's laboratory has not confirmed the 

 existence of this acetylene compound. 



Assumed Upon very slender evidence it has been advanced 3 



compound of t kat h y d rocyan i c ac id forms an easily broken up corn- 

 Hydrocyanic 1 ,! 1 11' 



acid with hae- pound with haemoglobin. 



mogiobin. If the acid be added to a solution of haemoglobin, on 



crystallizing out the latter it retains some of the hydrocyanic acid, 



1 See Hermann, "Ueber die Wirkungen des Stickstoffoxydgas auf das Blut." 

 Beichert und Du-Bois-Keymond's Archiv, 1865, p. 469. 



2 Bistrow u. Liebreich, Ber. d. deutsch. chem. Gesellschaft Berlin, 1868,^p. 220. 



3 Hoppe-Seyler, "Cyanwasserstoffhaemoglobinverbindungen." Med. Chem. Unter- 

 mchungen. Heft n. (1867) p. 207. 



