68 THE BODY AT WORK 



tions, it is difficult to isolate the effect of the drug from the 

 effects of improvements in the general regimen. Yet physi- 

 cians agree that iron accentuates the beneficial effects of fresh 

 air and improved diet. 



L 'When the surface of the body is struck, the effect of the blow 

 is marked at first by redness. There is nothing to show that 

 small bloodvessels have been ruptured and blood effused 

 beneath the skin. Next day the injured area is reddish-purple. 

 The bruise turns blue, green, yellow, and eventually disappears. 

 In the process of absorption, oxyhaemoglobin undergoes de- 

 composition. First its proteid constituent is removed, leaving 

 a coloured pigment containing iron, termed " hsernatin "; soon 

 reduced by loss of oxygen to haemochromogen. When Sir 

 George Stokes first described the spectrum of blood (cf. p. 185), 

 he showed that as haemoglobin may exist in an oxidized and in 

 a non-oxidized condition, distinguished by their spectra, so 

 also may the coloured residue which is left after the proteid 

 constituent has been removed from haemoglobin. This 

 coloured residue he termed, when oxidized, " haematin " ; when 

 not oxidized, " reduced haematin." Stokes's reduced haematin 

 is now termed " haemochromogen." Haemochromogen stands 

 for the coloured nucleus of haemoglobin. Although it is not 

 present in haemoglobin as haemochromogen hence we must not 

 speak of haemoglobin as made of a protein, x, plus haemo- 

 chromogen, y it is to its coloured residue that haemoglobin 

 owes its value as a carrier of oxygen. Later, iron is removed 

 from haemochromogen, leaving haematoidin, a substance often 

 found at the seat of old haemorrhages, where it may remain 

 unchanged for a very long time. Haematoidin is apparently 

 identical with the yellow pigment of bile, bilirubin. The 

 green colour which shows itself in the bruise seems to indicate 

 that the more oxidized bile-pigment, biliverdin, is formed in 

 the first instance. Red corpuscles, when destroyed in the 

 spleen, pass through transformations similar to those which 

 blood undergoes when effused beneath the skin. Their 

 protein is used by the phagocytes which eat them. Their iron 

 is reserved for the use of the blood-forming cells of the red 

 marrow of bone. The pigment which remains as the residue 

 of haemoglobin is carried by the splenic vein to the liver, which 

 secretes it as bile-pigment. So much of the bile-pigment as is 



