56 ORIGIN AND NATURE OF LIFE 



end of the spectrum and proceeding towards 

 the violet are named by the capital letters 

 of the alphabet, and some of the less marked 

 ones by the small letters. Such lines act as 

 landmarks in roughly assigning a position to 

 any given line, or absorption band, in a spec- 

 trum of a substance. In this way the spectro- 

 scope becomes a great assistant to the chemist, 

 and this is not merely true for the stellar 

 chemist : the physiological chemist or bio- 

 chemist can call in its aid to detect and 

 identify many of the coloured pigments of 

 high importance in the plant and animal 

 world. For example, the red colouring matter 

 of the blood so indispensable to life, which 

 carries round oxygen for the combustion of 

 the nutrition of the living cells derived from 

 the daily food, is identified when placed before 

 even a pocket spectroscope by two specific 

 and distinctive broad bands in the red to the 

 left of the D line mentioned above. When 

 the bio-chemist sees these two bands, he is 

 as certain that he has before him a fluid 

 containing blood, as any one in ordinary life 

 is of the presence of a well-known friend when 

 he looks him in the face. 



Just in the same way the stellar chemist 

 can say, there is the set of hydrogen lines, 

 there are the iron lines, and there the well- 



