CHEMICAL BASIS OF THE ANIMAL BODY. 1295 



a moderately strong solution of oxy-luemoglohin add ;i fr\v 

 drops of a dilute (-5 1-0 p.c.) solution of either of the salts and 

 warm very gently. If on examination with a spectroscope the 

 two bands of oxy-haemoglobin are still strongly visible, let the 

 mixture stand for a short time, and if the band characteristic 

 of methaemoglobin has not made its appearance add one or two 

 drops more of the solution of the salt and proceed as before. 

 As soon as the bands of oxy-hsemoglobin have markedly disap- 

 peared, acidulate very faintly and examine again. The band 

 which should now be visible as characteristic of methaemoglobin 

 lies in the red part of the spectrum, between C and D, nearer 

 to the former line. As already remarked its position is closely 

 similar to that of hsematin in acid solution, but comparison will 

 shew that it lies nearer D than does the haematin band, the 

 centre of the latter being situated at w. L. 640, while that of 

 the former is at \v. L. 630 (see Fig. 90, Nos. 4 and 5). 



In the preparation of large quantities of crystallized oxy- 

 hremoglobin from pig's blood it was observed that during the 

 recrystallizing essential to its purification a copious crop of 

 reddish-brown crystalline needles was obtained. These were 

 found on examination to be crystals of methtemoglobin. They 

 are most easily obtained if the oxy-hsemoglobin is first con- 

 verted into methsemoglobin by the action of potassium ferricy- 

 anide (one or two minute crystals of the salt to half a litre of 

 warm concentrated solution of oxy-hsemoglobin) ; the mixture 

 is then shaken until it has a dark brown colour, and is cooled to 

 after the addition of one quarter of its bulk of alcohol also 

 cooled to 0. They have also been obtained from the blood 

 of the dog, horse and otlier animals, and resemble in crystalline 

 form the crystals of oxy-haemoglobin from the same sources. 

 These crystals are doubly refracting, readily soluble in water 

 though less so than oxy-hsemoglobin, and the solution, unlike 

 that of the latter substance, yields a precipitate with basic lead 

 acetate in presence of ammonia ; they are identical in percent- 

 age composition with those of oxy-htemoglobin. 



The behaviour of methaemoglobin towards reducing agents 

 is interesting and also important as affording a means of dis- 

 crimination between this substance and haematin. If some 

 ammonium sulphide be added to an alkaline solution of metha-- 

 moglobin the mixture may be observed to yield the spectrum 

 of (reduced) hemoglobin, and on now shaking up with oxygen 

 (air) it shews the spectrum of oxy-hamioglobin. When a solu- 

 tion of haematin is similarly treated it yields the spectrum of 

 haemochromogen (reduced luematin) in alkaline solution (see 

 below). 



7. Haemocyanin. As previously stated (p. 1201) the blood- 

 plasma of many invertebrates contains haemoglobin in solution; 



