NITRIC OXIDE HAEMOGLOBIN. 241 



converted into a black shining mass, which when spread in thin layers 

 over porcelain appears of a greenish-brown colour. 



4. Aqueous neutral solutions of pure CO-haemoglobin, when heated 

 to boiling point, furnish a bright red precipitate, composed of coagulated 

 albuminous substances and CO-haemochromogen (Hoppe-Seyler). 



5. Solutions of carbonic oxide haemoglobin, treated with NO in the 

 absence of oxygen, are at once decomposed, and liberate CO (Hiifner). 



NITRIC OXIDE HEMOGLOBIN (NO-HEMOGLOBIN). 



Mode of preparation. So great is the affinity of nitric oxide for oxygen, 

 that, when it comes in contact with it, deep red fumes of nitrogen peroxide, N0. 2 , 

 is formed. When this gas comes in contact with water, the decomposition 

 indicated in the following equation occurs : 



But as all free acids decompose the colouring matter of the blood, before 

 causing nitric oxide to act upon blood certain precautions must be taken ; 

 for even if atmospheric oxygen be eliminated and nitric oxide caused to act 

 upon oxyhaemoglobin, nitrous oxide would be formed at the expense of the 

 oxygen of that body ; and next, by the action of water, nitric acid, which 

 would immediately decompose the haemoglobin. 



Two methods of proceeding are open to us (a) To add to the solution of 

 oxy haemoglobin which is to be subjected to the action of nitric oxide, sufficient 

 alkali to neutralise the nitric acid which will be formed. Such a solution 

 must be placed in a flask, permitting of the whole of the air above the solution 

 being driven out and replaced by a neutral gas, before allowing access to the 

 nitric oxide. After the latter has exerted its action, care must be taken again 

 to pass a neutral gas through the apparatus and solution, so as to remove all 

 traces of free nitric oxide. 



(b) The solution of oxyhaemoglobin is subjected to the long-continued 

 action of carbonic oxide, so as to form CO-haemoglobin and to expel nil traces 

 of dissolved oxygen. Otherwise, the process is constructed as described 

 under (a). This process would be certainly preferred, if it were desired to 

 crystallise the NO-compound. 



Physical and chemical characters. Blood saturated with nitric oxide 

 possesses almost as florid a colour as CO -blood, though Hermann says 

 that it does not present the slight bluish shade of the latter. It exhibits 

 no dichroism. Solutions of NO -haemoglobin, or diluted NO-blood, 

 exhibit a visible spectrum in which, as I have convinced myself, the 

 bands occupy precisely the position of the two oxyhsemoglobin bands. 

 In the photographic spectrum, however, the band in the extreme violet 

 exhibits absolute coincidence with that of CO -haemoglobin. 



NO-haemoglobin can be crystallised, and, as Hermann showed, the 

 crystals are identical with those of oxyhaemoglobin and CO-haemoglobin. 



ALLEGED (BUT PROBLEMATICAL) COMPOUNDS OF HEMOGLOBIN 



WITH GASES. 



1. With hydrocyanic acid. The most discrepant statements have 

 been made in reference to the very simple question whether hydrocyanic 

 acid added to, or passed through, blood affects the characters of its absorption- 

 spectrum. In spite of these, it may be definitely stated that, at ordinary 

 temperatures, and when acting for moderate periods, hydrocyanic acid leads 

 VOL. i. 1 6 



