BLOOD. 203 



old turpentine. The customary blue color will be observed in the 

 presence of blood. 



(d) Benzidine Reaction. Make this test according to directions 

 given on p. 196. 



(e) Acid Hcematin. If the stain fails to dissolve in water ex- 

 tract with acid alcohol and examine the spectrum for absorption 

 bands of acid hsematin (see Absorption Spectra, Plate II). 



VI. Spectroscopic Examination of Blood. 

 (For Absorption Spectra see Plates I. and II.) 



Either the angular-vision spectroscope (Figs. 62 and 63, page 

 204) or the direct-vision spectroscope (Fig. 61, below) may be 

 used in making the Spectroscopic examination of the blood. For a 

 complete description of these instruments the student is referred 

 to any standard text-book of physics. 



i. Oxyhaemoglobin. Examine dilute ( i : 50) defibrinated blood 

 spectroscopically. Note the broad absorption-band between D and 

 E. Continue the dilution until this single broad band gives place 

 to two narrow bands, the one nearer the D line being the narrower. 

 These are the typical absorption-bands of oxyhaemoglobin obtained 

 from dilute solutions of blood. Now dilute the blood very freely 

 and note that the bands gradually become more narrow and, if the 

 dilution is sufficiently great, they finally entirely disappear. 



FIG. 61. 





DIRECT-VISION SPECTROSCOPE. 



2. Haemoglobin (so-called Reduced Haemoglobin). To blood 

 which has been diluted sufficiently to show well defined oxyhsemo- 

 globin absorption-bands add a small amount of Stokes' reagent. 1 

 The blood immediately changes in color from a bright red to violet- 

 red. The oxyhaemoglobin has been reduced through the action of 

 Stokes' reagent and haemoglobin (so-called reduced haemoglobin) 

 has been formed. This has been brought about by the removal 



1 Stokes' reagent is a solution containing 2 per cent ferrous sulphate and 

 3 per cent tartaric acid. When needed for use a small amount should be 

 placed in a test-tube and ammonium hydroxide added until the precipitate 

 which forms on the first addition of the hydroxide has entirely dissolved. This 

 produces ammonium f err o tar irate which is a reducing agent. 



