246 HAEMOGLOBIN. 



added to a litre of saturated aqueous solution of crystals of oxylisemoglobin, 

 and after the conversion into methaemoglobin lias occurred, about 25 per cent, 

 of alcohol added. The mixture is then exposed to a temperature below C. 

 I succeeded in recrystallising methsemoglobin prepared by the action of 

 potassium nitrite and of ethyl and amyl nitrites on oxyhseinoglobin. 



Chemical and physical characters. Crystals of methsemoglobin are 

 more sparingly soluble than those of oxyhaemoglobin, and the colorific 

 intensity of their solutions is less. 



It is to be noted that, whilst solutions of reduced and oxyhaemoglobin 

 are not precipitated by either neutral or basic lead acetates, these 

 reagents added cautiously, with careful avoidance of an excess, precipi- 

 tate methcemoglobin, hcematin, and hcemytoporphyrin, and may be em- 

 ployed for the separation and detection of traces of oxy haemoglobin 

 when mixed with and concealed by any of the above-mentioned bodies. 



Solutions of methaemoglobin, when of a neutral or a slightly acid 

 reaction, possess a chocolate-brown colour. When the solution is 

 rendered alkaline, its colour changes to red without a tinge of the 

 chocolate-brown. 



The acid solution is found to present a spectrum in which the oxy- 

 heemoglobin bands a and /3 are very weak or even not visible, whilst an 

 absorption-band is seen in the red between C and 1), and nearer the 

 former. This band occupies nearly, though by no means exactly, the 

 position of a similar band in the spectrum of acid haematin (see Plate 

 II., Spectrum 5). 



On now rendering the solution alkaline by means of ammonia, the 

 band in the red disappears, and is replaced by a faint absorption-band 

 immediately on the red side of D. By changing the reaction of the 

 solution, the alterations in its colour and spectrum may be repeated 

 indefinitely (Garngee). 



If a solution of methaemoglobin be placed in a deep test tube, in 

 front of a spectroscope, and arrangements be made for allowing a stream 

 of solution of ammonium sulphide to flow to the bottom of the 

 liquid, it can be readily shown that at the very moment of the 

 contact of the reducing and the methsemoglobin solution, the spec- 

 trum of oxyhaemoglobin appears ; to be subsequently and much more 

 slowly replaced by that of reduced haemoglobin, which in its turn, 

 when shaken with air, yields oxyhaemoglobin. 



A study of the photographic spectrum of methaemoglobin has led 

 me to results of great interest. The conversion of oxyhaemoglobin into 

 inethaemoglobin is attended by a shifting of the band of Soret from the 

 extreme violet to the ultra-violet properly so called (Fig. 36). The most 

 persistent part of the band in very dilute solutions, coincides, indeed, 

 with the H and K bands, but the band extends more and more into the 

 ultra-violet, as the concentration of the solution increases. The position 

 and characters of this band in the case of methsemoglobin absolutely 

 corresponds with those of the acid compounds of haematin, and not 

 with those presented by haemoglobin and its compounds, or by 

 haemochromogen (see Fig. 38). 



This spectroscopic character certainly seems to lend weight to the 

 evidence of other kinds, which indicates that methaemoglobin is a first 

 product of the decomposition of the oxyhaemoglobin molecule, and that 

 this is a decomposition which leads to the separation of a compound of 

 haematin, and not of haemochromogen. Hoppe-Seyler, indeed, expressed 



