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A TEXTBOOK OF PHYSIOLOGY 



In old blood-clots, flat, lozenge-shaped crystals, of a bright red 

 colour, are often found. This is an iron-free derivative of haemoglobin, 

 isomeric with bilirubin, and called haematoidin. 



Besides the derivatives which have been studied with the spectro- 

 scope, there is another derivative of haematin haemin, which is identi- 

 fied by the rhombic form and brown colour of its crystals. Haemin 

 is the hydrochloride of haematin, and is prepared by heating blood 

 with glacial acetic acid. 



The Estimation of Haemoglobin. By estimating the haemoglobin 

 in the blood we can measure the oxygen-carrying power, and make 

 comparative tests of the blood in cases of anaemia, etc. The measure- 

 ment is made by the use of an instrument known as the hsemoglobin- 

 ometer. In this country, apparatus shown in Fig. 23 is chiefly 

 employed. This contains a sealed tube (D) containing coal-gas and 



FIG. 23. HALDAXE-GOWERS' HJEMOGLOBINOMETER. 



a standard solution of human blood (1 in 200); the haemoglobin, 

 being combined with CO, makes the solution a stable one. A 

 small quantity (up to mark 20 or so) of distilled water (carried in a 

 bottle (A) furnished with a pipette stopper) is placed in the graduated 

 tube C. Blood is taken from the patient, either from the finger-tip 

 or the lobe of the ear, and sucked up into the pipette B to the mark 20, 

 and then carefully added to the water in the graduated tube. The 

 distilled water lakes, the blood, and a solution of oxyhaemoglobin is 

 formed. This is converted into COHb by passing coal-gas into the 

 tube and shaking it with the solution. Or the distilled water in the 

 bottle A may be previously saturated with CO by bubbling coal-gas 

 through it. All that now remains is to dilute carefully the solution 

 of COHb with water until it is of the same tint as the standard 

 tube when compared against a white background. The percentage 

 . of Hb is registered by the graduations in the tube. . The standard is 



