CHEMICAL BASIS OF THK ANIMAL BODY. 229 



are mo<t 'a-ily nl.tained if the oxy-hrcmoglobin is first converted 



into metha-moglohin by the action of potassium ferric\anide (mi,, 

 or two minute crystals of tin- salt to half a litre of warm con- 

 centrated sulution of oxy-hii-nioglobin) ; the mixture i-. then 

 shaken until it lias a dark-brown colour and is cooled to 

 tin- addition of one quarter of its bulk of alcohol also cooled to 

 0. They have also been obtained from the bl 1 of tin- 

 horse .- and other animals, 3 and resemble in crystalline form the 



crystals of Mnr-httmoglobin from the same sources. These crystals 



arc doubly refracting, readily soluble in water, though less so than 

 oxy-luemoglobin, and the solution, unlike that of the latter sub- 

 stance, yields a precipitate with basic lead acetate in presence of 

 ammonia ; they are identical in percentage composition with those 

 of oxy-luemoglobin. The behaviour of metha-moglobin towards 

 reducing agents is interesting and also important as affording a 

 means of discrimination between this substance and hit-matin. 

 If some ammonium sulphide be added to an alkaline solution of 

 methcemoglobin, the mixture may be observed to yield the spectrum 

 of i reduced) ha-moglobin ; and on now shaking np with o 

 (air it sln>w> tlie spectrum of OXV-hftmqglobilL "When a solution 

 of ha matin is similarly treated it yields the spectrum of ha mo- 

 chromogen (reduced hematin) in alkaline solution (see below). 

 "While the close relationship of methsemoglobin to oxy-ha-moglobin 

 is thus clearly shown, very great differences of opinion have ex- 

 isted as to the exact nature of that relationship. Three \ 

 have been put forward. 1. That meth&emoglobin is more highly 

 oxjdised than OXY-hffimoglobilL -. That it is le s highly oxidised. 

 .". That it is united with exactly the same amount of oxygen as 

 is oxy-luemoglobin i only in a more stable combination. Th- 

 ins to have been based on the ready production of 

 nietha-moglobin by oxidising agents and on the statement that 

 when metha-moglohin is reduced it yields //,*/ oxy-h;emoglobin 

 and then ha-moglohin. The second view iv-ted on the possibility 

 of obtaining metbttmoglobui by the prolonged action of a \acuum 

 or the -bolter action of palladium saturated with hydi 

 and on the statement that by reducin it passe 



to ha-moglobin \\ithout tin- intermediate appearance of 

 ha-moglnbin. The third view, which now appears to be generally 



ted, H derived fr-Ull obs,-r\ at j 'US of the aillolint - 



which can be pumjied out from a mixture of meth.emoglobin ami 

 oxy-ha-moglubin of known composition. 1 and from the amount of 



' IIufn.T. //././. Bd.Tm.(lM4),fl 'IMV .lu,!,.rl,..ln, / / IM XX. (1884), 



> in 



,n..t. .1 l.y Jii<lcrli<-]in, lor. , 



illilmrt-.ii. Quart. ./'/. .I/;. \\\m (isssi. j. i'ui (.iv... rapid 



iiii-ih<><l fur inirrsrii]iii- pnrpoHoti ; <iml t'nthoJ p. 28O. 



4 Tlif liti-ratiip- i-f tin- .li-|,iiti' i* fully qt -9 IT 



I',.! \\\i >n. -.: - mini: lii-rntnre to 



(18IU) has l.c.'n u'iv.-n /-i^,m in tli" ;ili<i\i- ;irr<>uiil "f this -tiih-' 



