CH. X.] CARBOXYHAEMOGLOBIN. 245 



the latter case, that the bright scarlet colour of oxyhaemoglobin 

 gives place to the less vivid colour of reduced haemoglobin. Ex- 

 amine the solution spectroscopically. There is a single broad 

 band in the green which overlaps the space enclosed by the two 

 bands of oxyhaemoglobin, and is fainter than either. Its centre is 

 about X 565. 



NOTE. Stokes' fluid is prepared as follows : dissolve 3 grams, of ferrous 

 sulphate in cold water : add a cold aqueous solution of 2 grams, of tartaric acid 

 and make the solution up to 100 cc. with water. Immediately before use add 

 strong ammonia until the precipitate first produced is redissolved. It rapidly 

 absorbs atmospheric oxygen and must, therefore, be freshly prepared. Its 

 great advantage over ammonium sulphide is that it can be used in the cold, 

 whilst with the sulphide the solution must be warmed. 



294. Place your thumb over the top of the test-tube contain- 

 ing the reduced haemoglobin and shake vigorously. Examine 

 immediately with the spectroscope, and note that the two bands of 

 oxyhaemoglobin have reappeared owing to the oxidation of the 

 haemoglobin by the oxygen of the air. If the tube be allowed to 

 stand for a short while, reduction may occur again from excess of 

 reducing reagent present. 



295. Carboxyhaemoglobin. Obtain some CO-haemoglobin 

 that has been prepared by passing a stream of carbon monoxide or 

 coal-gas through a solution of oxyhaemoglobin. Notice the peculiar 

 bluish tinge of the solution. Examine a portion spectroscopically, 

 and, if necessary, add water till two well-marked bands are visible. 

 Note that they are very similar to the two bands of oxyhaemoglobin. 

 Accurate observation, however, will show that they are both 

 slightly nearer the violet end of the spectrum, the middle of a 

 being X 572 and of ft X 535. 



NOTES. i. A small amount of caprylic alcohol added to the blood 

 facilitates the preparation of Hb-CO in preventing excessive frothing. 



2. If the student can satisfy himself of the difference between the position 

 of the absorption bands of Hb-O 2 and Hb-CO, he can always obtain a sample 

 of Hb-O 2 for comparison with an unknown solution by pricking his finger. 



296. Take a portion of the diluted solution of CO-haemoglobin 

 just examined, treat it with a few drops of ammonium sulphide, 

 warm in a bath at 50 C. for three minutes and examine with the 

 spectroscope. No change takes place in the spectrum. (Distinction 

 from oxyhaemoglobin.) 



