x NO-HEMOGLOBIN 503 



meat might be due to the presence of nitrite, and Robert l attributed 

 the red colour to a union of nitrites with methaemoglobin. Haldane 2 

 then showed that the colour of uncooked red meat is simply due to 

 pure NO-haemoglobin, while in boiled meat it is due to NO-haemo- 

 chromogen. Nitric oxide first reduces haematin to haemochromogen, 

 and then combines with the latter. Nitric oxide-haemochromogen was 

 first prepared by Linossier 3 by bubbling nitric oxide through 

 haematin solutions. According to Haldane, NO acts on oxy haemo- 

 globin, reduced haemoglobin, and methaemoglobin in this way : 



(1) Haemoglobin readily combines either with nitric oxide to form 

 NO-haemoglobin or with nascent oxygen to form methaemoglobin. 



(2) Nitrous acid easily yields up simultaneously nitric oxide and 

 oxygen. 



(3) Nitric oxide readily combines with either oxygen or haemo- 

 globin. 



If no extraneous oxygen is present, as when reduced haemoglobin is 

 acted on by the nitrite, both the nitric oxide and the oxygen yielded 

 up by the nitrite will combine with the haemoglobin ; and as far 

 more nitric oxide than oxygen is yielded up, more NO-haemoglobin 

 than methaemoglobin will be formed. On the other hand, when oxy- 

 haemoglobin or methaemoglobin is acted on, the nitric oxide will be 

 free either to combine with haemoglobin or with the extra oxygen 

 available, and a balance will be struck depending on the relative 

 strengths of the various affinities. The conversion of nitrates into 

 nitrites is brought about by the tissues themselves, as they contain a 

 reducing substance which acts even in the presence of antiseptics. 



NO-haemoglobin forms crystals which are isomorphic with those 

 of oxyhaemoglobin its solutions are bright red and do not 

 exhibit dichroism, according to Hermann. NO-haemoglobin shows 

 two absorption-bands which are less defined than are those of oxy- 

 haemoglobin, and the band near D extends beyond D towards the 

 red ; 4 the absorption-band in the violet is the same as in the case of 

 CO-haemoglobin, according to Gamgee. NO-haemoglobin is as difficult 

 to reduce as is CO-haemoglobin. 



Haldane, Makgill, and Mavrogordato 5 have shown the poisonous 

 action of nitrites to be due to their action on the haemoglobin, and the 



1 R. Robert, Pfluger's Arch. 82. 603 (1900). 



2 Haldane, Journ. of Hygiene, 1. 115 (1901). 



3 Linossier, Crnn.pt. Rend. 104. 1296 (1887). 



4 Haldane, Journ. of Hygiene, 1. 115 (1901). See also R. Robert, Pflugers Arch* 

 82. 603 (1900). 



5 J. Haldane, R. H. Makgill, and A. E. Mavrogordato, Journ. of Physiol, 21 

 160 (1897). 



