CH.XXVI.] COMPOUNDS OF H-EMOGLOBIN. 435 



truni " to Prof. Gamgee, through whose kindness I am enabled 

 to present reproductions of two of his numerous photographs 

 (figs. 366 and 367). 



Methsemoglobin. This may be produced artificially in various 

 ways, as by adding potassium ferwcyanide or amyl nitrite to blood, 

 and as it also may occur in certain diseased conditions in the 

 urine, it is of considerable practical importance. It can be 

 crystallised, and is found to contain the same amount of oxygen 

 as oxyhsemoglobin, only combined in a different way. The oxygen 

 is not removable by the air-pump, nor by a stream of neutral gas 

 like hydrogen. It can, however, by reducing agents like am- 

 monium sulphide, be made to yield hrernoglobin. Methaemoglobin 

 is of a brownish-red colour, and gives a characteristic absorption 

 band in the red between the C and D lines (spectrum 7 in 

 coloured plate). In dilute solutions other bands can be seen. 



Potassium ferricyanide is the most convenient re-agent for making 

 methaemoglobin. It is, however, necessary to mention that it produces 

 another effect as well, namely, it causes an evolution of gas, if the blood 

 has been previously laked by the addition of an equal quantity of water. 

 This gas is oxygen ; in fact, all the oxygen combined as oxy haemoglobin is 

 discharged, and this may be collected and measured ; the addition of a 

 small amount of sodium carbonate or ammonia to the blood is necessary 

 to prevent the evolution of any carbonic acid. This discharge of oxygen 

 from oxyhsemoglobin is at first sight puzzling, because, as just stated, 

 methaemoglobin contains the same amount of oxygen that is present in 

 oxyhaemoglobin. What occurs is that after the oxygen is discharged from 

 oxyhaemoglobin, an equal quantity of oxygen, due to the oxidising action 

 of the re-agents added, takes its place ; this new oxygen, however, is com- 

 bined in some way different from that which was previously united to the 

 haemoglobin. (Haldane.) 



Carbonic oxide haemoglobin may be readily prepared by 

 passing a stream of carbonic oxide or coal gas through blood or 

 through a solution of oxyhsemoglobin. It has a peculiar cherry- 

 red colour. Its absorption spectrum is very like that of oxy- 

 hsemoglobin, but the two bands are slightly nearer the violet end 

 of the spectrum (spectrum 4 in coloured plate). Reducing 

 agents, like ammonium sulphide, do not change it ; the gas is 

 more firmly combined than the oxygen in oxyhsemoglobin. 

 CO-hjemoglobin forms crystals like those of oxyhccmoglobin. It 

 resists putrefaction for a very long time. 



Carbonic oxide is given off during the imperfect combustion of 

 carbon such as occurs in charcoal stoves or during the explosions 

 that occur in coal mines : it acts as a powerful poison by 

 combining with the haemoglobin of the blood, and thus inter- 

 feres with normal respiratory processes. The bright colour of the 



F p 2 



