CH. X.] HAEMATIN. 247 



2. The reaction is peculiar in that an amount of oxygen is evolved 

 equivalent to that held in combination by the oxyhaemoglobin, although 

 methaemoglobin contains the same percentage of oxygen as oxyhaemoglobin. 

 This reaction is the basis of the modern method of estimating the amount of 

 oxygen in the blood. 



The reaction might be represented by the following equation : 



Oxyhaemoglobin. From ferricyanide Methaemoglobin. Gas 



and water. 



The oxygen is represented as being in a different state of combination in 

 methaemoglobin, since it cannot be removed by submitting the compound to a 

 vacuum. 



3. When methaemoglobin is treated with a reducing reagent, the first 

 change that occurs is that the linkage of the oxygen atoms reverts to that of 

 oxyhaemoglobin; later, the oxygen is removed and reduced haemoglobin 

 formed. 



301. Acid haematin. To 5 cc. of water add four drops of 

 defibrinated blood and five drops of strong acetic acid and heat. 

 The colour changes to brown ; and the solution shows an absorption 

 band in the red, which is further from the D line than that of 

 methaemoglobin. Its centre is about X 650. 



302. Acid haematin in ethereal solution. Treat a few cc. 

 of defibrinated blood with one drop of strong hydrochloric acid and 

 a few cc. of acetic acid : extract this with about 5 cc. of ether by 

 gentle shaking, pour the ether into a clean tube and examine it with 

 the spectroscope. There is a prominent band in the red (centre X 

 638) ; on dilution with ether three other bands can be seen ; a very 

 narrow one with centre X 582 ; a broad one stretching from about 

 ^ 555 to X 530 and another from X 512 to X 498. 



303. Alkaline haematin. To 5 cc. of alcohol add 3 drops of 40 

 per cent, soda and 2 drops of defibrinated blood. Mix and heat till 

 the alcohol just boils. Add an equal volume of water and examine 

 spectroscopically. A prominent band is seen in the red, stretching 

 from X 620 to X 595. On the blue- ward side is a shading extending 

 to about X 570. The blue end of the spectrum may be absorbed. 



304. Alkaline haematin in alcohol. Mix defibrinated blood 

 into a thin paste with solid potassium carbonate and evaporate to 

 complete dryness on a water bath. Powder the residue, boil with 



