2O6 PHYSIOLOGICAL CHEMISTRY. 



to the left of D and, if the dilution is sufficiently great, also ob- 

 serve the two rather faint bands lying between D and E in some- 

 what similar positions to those occupied by the absorption bands 

 of oxy haemoglobin. Add a few drops of Stokes' reagent to the 

 methaemoglobin solution while it is in position before the spectro- 

 scope and note the immediate appearance of the oxyhaemoglobin 

 spectrum which is quickly followed by that of haemoglobin. 



5. Alkaline Methaemoglobin. Render a neutral solution of 

 methsemoglobin, such as that used in the last experiment (4), 

 slightly alkaline with a few drops of ammonia. The solution be- 

 comes redder in color, due to the formation of alkaline methaemo- 

 globin and shows a spectrum different from that of the neutral 

 body. In this case we have a band on either side of D, the one 

 nearer the red end of the spectrum being much the fainter. A 

 third band, darker than either of those mentioned, lies between D 

 and E somewhat nearer E. 



6. Alkali Haematin. Observe the spectrum of the alkali hae- 

 matin prepared in Experiment 16 on page 199. Also make a 

 spectroscopic examination of a freshly prepared alkali haematin. 1 

 The typical spectrum of alkali haematin shows a single absorption- 

 band lying across D and mainly toward the red end of the spectrum. 



7. Reduced Alkali Haematin or Haemochromogen. Dilute 

 the alkali haematin solution used in the last experiment (6) to 

 such an extent that it shows no absorption band. Now add a few 

 drops of Stokes' reagent and note that the greenish -brown color 

 of the alkali haematin solution is displaced by a bright red color. 

 This is due to the formation of haemochromogen or reduced alkali 

 haematin. Examine this solution spectroscopically and observe the 

 narrow, dark absorption-band lying midway between D and E. If 

 the dilution is not too great a faint band may be observed in the 

 green extending across E and b. 



8. Acid Haematin. To some defibrinated blood add half its vol- 

 ume of glacial acetic acid and an equal volume of ether. Mix 

 thoroughly. The acidified ethereal solution of haematin rises to the 

 top and may be poured off and used for the spectroscopic exam- 

 ination. If desired it may be diluted with acidified ether in the 

 ratio of one part of glacial acetic acid to two parts of ether. A 

 distinct absorption-band will be noted in the red between C and 



Alkali hsematin may be prepared by mixing one volume of a concentrated 

 potassium hydroxide or sodium hydroxide solution and two volumes of dilute 

 ,(1:5) defibrinated blood. This mixture should be heated gradually almost to 

 boiling, then cooled and shaken for a few moments in the air before examination. 



