THE BLOOD. 22/ 



Methemoglobin. Oxyhemoglobin in solution or in crystal 

 form, alone or in presence of certain reagents, shows a great 

 tendency to pass over into this modification which contains 

 just as much oxygen as the original, held, however, in stable 

 combination. Under the air pump methemoglobin does not 

 give up any oxygen, while from oxyhemoglobin nearly the 

 whole of the extra molecule may be abstracted. While this 

 formation of methemoglobin takes place spontaneously it is 

 greatly hastened by the action of several substances, some of 

 which are oxidizing agents, while others are reducers. Of the 

 oxidizing substances ozone, potassium permanganate, potas- 

 sium chlorate, iodine, potassium ferricyanide and nitrates have 

 been used, while such reducing agents as pyrogallol, pyro- 

 catechol, hydroquinol and hydrogen even, acting on the blood 

 have brought about a formation of the stable methemoglobin. 

 Certain substances given as remedies have the power of con- 

 verting the oxyhemoglobin into methemoglobin. Amyl ni- 

 trite, acetanilid and nitrobenzene may be mentioned here. 

 The poisonous action of large doses of potassium chlorate has 

 long been supposed to be due in part to the same reaction. 



Solutions of methemoglobin are not bright red but reddish 

 brown, and the crystalline substance is also bro\vn. The color 

 of an alkaline solution is red, but this is not due to a recon- 

 version into oxyhemoglobin. Certain reducing agents have 

 the power of gradually changing the methemoglobin back into 

 oxyhemoglobin and then into reduced hemoglobin. Am- 

 monium sulphide and Stokes' reagent work in this way. The 

 conversion may be followed by aid of the spectroscope. 



A product known as acid hemoglobin is formed by the action 

 of weak acids on hemoglobin. This appears to be a step in 

 the formation of methemoglobin, the spectrum of which it re- 

 sembles. With strong acids decomposition takes place and 

 hematin results. 



Hematin. It has been already explained that hemoglobin 

 breaks up readily into globin, about 96 per cent, and hematin, 

 about 4 per cent. This decomposition follows, as just men- 



