METH^EMOGLOBIN. 283 



crystals are as a rule isomorphous with the corresponding oxyhsemo- 

 globin crystals, but are darker, having a shade toward blue or purple, 

 and are decidedly more pleochromatic. The haemoglobin from horse- 

 blood has also been obtained by UHLIK 1 in hexagonal plates. Its 

 solutions in water are darker and more violet or purplish than solu- 

 tions of oxyhsemoglobin of the same concentration. They absorb the 

 blue and the violet rays of the spectrum in a less marked degree, but 

 strongly absorb the rays lying between C and D. In proper dilution 

 the solution shows a spectrum with one broad, not sharply denned band 

 between D and E, whose darkest part corresponds to the wave-length 

 X = 559 (spectrum Plate, 2). This band does not lie in the middle 

 between D and E, but is toward the red end of the spectrum, a little 

 over the line D. This pigment also gives a band in the ultra-violet, 

 X = 429. A haemoglobin solution actively absorbs oxygen from the air 

 and is converted into an oxyhsemoglobin solution. 



A solution of oxyhaemoglobin may be easily converted into a solution 

 having the spectrum of haemoglobin by means of a vacuum, by passing 

 an indifferent gas through it, or by the addition of a reducing substance, 

 as, for example, an ammoniacal ferrous-tartrate solution (STOKES' reduc- 

 tion liquid). If an oxyhaemoglobin solution or arterial blood is kept in 

 a sealed tube, we observe a gradual consumption of oxygen and a reduc- 

 tion of the oxyhaemoglobin into haemoglobin. If the solution has a 

 proper concentration, a crystallization of haemoglobin may occur in the 

 tube at lower temperatures (HUFNER 2 ) . 



Methaemoglobin. This name has been given to a coloring-matter 

 which is easily obtained from oxyhaemoglobin as a transformation prod- 

 uct and which has been correspondingly found in transudates and cystic 

 fluids containing blood, in urine in haematuria or haemoglobinuria, and 

 also m urine and blood on poisoning with potassium chlorate, amyl 

 nitrite or alkali nitrite, and many other bodies. 



Methaemoglobin does not contain any oxygen in molecular or dis- 

 sociable combination, but still the oxygen seems to be of importance in 

 the formation of methaemoglobin, because it is formed from oxyhsemo- 

 globin and not from haemoglobin in the absence of oxygen or oxidizing 

 agents. If arterial blood be sealed up in a tube, it gradually consumes 

 its oxygen and becomes venous, and by this absorption of oxygen a little 

 methaemoglobin is formed. The same occurs on the addition of a small 

 quantity of acid to the blood. By the spontaneous decomposition 

 of blood some methaemoglobin is formed, and by the action of ozone, 

 potassium permanganate, potassium ferricyanide, chlorates, nitrites, 



1 Pfliiger's Arch., 104. 



2 Zeitschr. f. physiol. Chem., 4; see also Uhlik, 1. c. 



