THE BLOOD. 75 



methaemoglobin is first converted into an oxyhaemoglobin and then 

 into a haemoglobin solution by reducing substances, while HOPPE- 

 SEYLER claims that it is converted directly into a haemoglobin 

 solution. 



Methaemoglobin has the same constitution as oxyhaemoglobin 

 (HiiFNEE and OTTO). It was first shown by them that it crystal- 

 lizes in brownish-red needles, prisms, or six-sided plates. It dissolves 

 easily in water ; the solution has a brown, color and becomes a 

 beautiful red on the addition of alkali. The solution of the pure 

 substance is not precipitated by lead acetate alone, but by lead 

 acetate and ammonia. The absorption-spectrum of a watery or 

 acidified solution of methaemoglobin is very similar to that of 

 haematin in acid solution, but is easily distinguished from the 

 latter since, on the addition of a little alkali and a reducing 

 substance, the former passes over to the spectrum of reduced 

 haemoglobin, while a haematin solution under the same conditions 

 gives the spectrum of an alkaline haemochromogen solution (see 

 below). Methaemoglobin in alkaline solution shows two absorption- 

 bands which are like the two oxyhaemoglobin bands, but they differ 

 from these in that the band ft is stronger than a. By the side of 

 the band a and united with it by a shadow lies a third, fainter 

 band between C and D, near to D. 



Crystallized methaemoglobin may be easily obtained by treating 

 a concentrated solution of oxyhaemoglobin with a sufficient quanti- 

 ty of concentrated potassium ferricyanide solution to give the mix- 

 ture a porter-brown color. After cooling to C. add vol. cooled 

 alcohol and allow the mixture to stand a few days in the cold. The 

 crystals may be easily purified by recrystallizing from water by the 

 addition of alcohol. 



Carbon monoxide methaemoglobin has been prepared by WEYL and v. 

 ANSEP by the action of potassium permanganate on carbon monoxide haemo- 

 globin. Sulphur methaemoglobin is the same given by HOPPE-SEYLER to that 

 coloring matter which is formed by the action of sulphuretted hydrogen on 

 oxyhaemoglobin. ^ The solution has a greenish-red, dirty color and shows an 

 absorption-band in the red. This coloring matter is claimed to be the greenish 

 color seen on the surface of putrefying flesh. 



Decomposition products of the blood coloring matters. By 

 its decomposition haemoglobin yields, as above stated, albumin and 

 a ferruginous coloring matter as chief products. If the de- 

 composition takes place in the absence of oxygen, a coloring matter 



