22 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



MetliaemogloMn. 



Preparation. On treating a concentrated solution of oxy 

 haemoglobin with a sufficient quantity of a concentrated 

 solution of potassium ferricyanide to give the mixture a 

 porter-brown color, methaemoglobin will be formed. After 

 cooling to 0. add i vol. alcohol cooled to C., and allow 

 the mixture to stand a few days in the cold. The crystals ob- 

 tained may be easily purified by recrystallization from water 

 by the addition of alcohol. (Pig's blood is better adapted for 

 the preparation of methsemoglobin than dog's blood.) 



Properties.- Methaemoglobin crystallizes in brownish-red 

 needles, prisms, or six-sided plates. It dissolves readily in 

 water, and this solution becomes red on the addition of alkali. 

 The spectrum of methaemoglobin shows three absorption- 

 bands, one in the red about half way between C and D, the 

 other two between D and E, which resemble the position of the 

 oxyhgemoglobin lines, but on careful measurement are found 

 to be different. 



Fibrin Ferment. 



Preparation. Blood-serum is mixed with 10 to 15 times 

 its volume of absolute alcohol ; by this means the proteids are 

 precipitated, as also the ferment. The precipitate is allowed 

 to stand a few months with the alcohol, which renders the 

 proteids insoluble. Filter the precipitate off and dry in de- 

 siccator over sulphuric acid. The ferment is separated from 

 the other bodies by extracting with water, which dissolves the 

 ferment. (A. Schmidt.) 



Properties. A solution of the ferment will coagulate peri- 

 cardial and similar fluids or solutions of fibrinogen. It is 

 most active at about 40 0. It is diminished in action at C., 

 and entirely destroyed on heating its solutions to 73-75 C. 



