BLOOD AND LYMPH 



211 



When light from the sun is allowed to pass through 

 solutions of blood pigments, certain parts of the solar spectrum 

 are absorbed, and when the spectrum is examined dark bands 

 the absorption bands are seen. In a weak solution of oxy- 

 haemoglobin a dark band is seen in the green and another in 

 the yellow part of the spectrum between Frauenhofer's lines 

 D and E, while the violet end of the spectrum is absorbed 

 (fig. 103). These bands may be broadened or narrowed by 

 strengthening or weakening the solution. When the oxygen 

 is taken away and the purple reduced haemoglobin is formed, 

 RED. YELLOW. GREEN. BLUE. 



Carbon-monoxide ) 



Haemoglobin . v 



Oxyhsemoglobin . ) 



Haemoglobin 



llethsemoglobin . \ 

 Acid Hicmatin . / 



Reduced Alkaline 



I In.' mat in . 



FIG. 103. Spei-tra of the more important Blood Pigments and their more 

 important derivatives. (The Spectrum of Acid Haematin is not identical 

 with that of Methaemoglobin.) 



a single broad band between D and E takes the place of the 

 two bands (fig. 103). (Chemical Physiology.} 



The property of taking oxygen from the air and of again 

 giving it up at a moderate temperature and under a low 

 pressure of oxygen is the great function of the blood pigment 

 in the body. The haemoglobin plays the part of a middle- 

 man between the air and the tissues, taking oxygen from the 

 one and handing it on to the others. (Chemical Physiology.} 



Haemoglobin constitutes about 13 or 14 per cent, of the 

 blood, but in various diseases its amount is decreased. The 

 best method of estimating its amount is by Haldane's Haemo- 

 globinometer. This consists of two tubes of uniform calibre, 



