162 



ESSENTIALS OF PHYSIOLOGY. 



* 



FIG. 52. Hsemiii crystals, magni- 

 fied. (Preyer.) From Quain's 

 Anatomy. 



haemoglobin, provided the globin has not been destroyed by the re- 

 agents used to dissociate the haemoglobin molecule. 



If haematin (or haemoglobin) be treated with a strong mineral acid, 



iron-free haematin or hcematoporphyrin, 

 C 34 H 38 N 4 6 , is formed. Acid solutions 

 of this substance show a spectrum 

 with two absorption bands, one on 

 either side of the D line, that to the 

 red side being the narrower (fig. 51). 

 The spectrum of alkaline solutions is 

 somewhat similar to that of methae- 

 moglobin (fig. 51). 'Haematoporphyrin 

 occurs occasionally in the urine in 

 sulphonal poisoning, its spectrum in 

 such cases being of the alkaline type. 

 Two similar substances are found in 

 the body, hcematoidin in old blood 

 clots, and bilirubin, the primary bile 

 pigment ; they are formed from haemo- 

 globin and are said to be identical, each containing one atom less of 

 oxygen than does haematoporphyrin. 



THE ESTIMATION OF HAEMOGLOBIN. 



The estimation of the amount of haemoglobin contained in a sample 

 of blood is usually carried out by a colorimetric method. The apparatus 

 used is called a haemoglobinometer, and consists of two tubes, one of 

 which is sealed and contains a standard dilution of ox blood, the haemo- 

 globin of which has been converted into carboxyhaemoglobin. A little 

 distilled water and a measured quantity of the blood to be examined 

 are placed in the second tube, which is graduated. The blood, laked 

 by the water, is exposed to coal gas, and in this way the haemoglobin 

 is converted into carboxyhaemoglobin. It is then diluted with distilled 

 water till the tints of the two tubes are alike, and the level of the fluid 

 in the graduated tube is read. If the latter is at the figure 100, the 

 amount of haemoglobin is said to be normal or 100 per cent. If it is 

 over 100, the blood is abnormally rich in haemoglobin ; if below 100, it 

 is deficient in haemoglobin. The figure 100 per cent, is purely empirical, 

 and the amount of haemoglobin actually present in blood is normally 

 about 14 per cent. 



If the number of red corpuscles in the blood is ascertained at the same 

 time, the value of the haemoglobin content of each corpuscle can be stated. 

 Thus if the number of corpuscles is the normal five millions per cubic 



