THE LIVER AND BLOOD PIGMENTS. 



337 



product haematoporphyrin. As bilirubin and haematoporphyrin 

 are fundamentally identical, the presence of the former in the 

 bile must be the result of a similar process in the liver. That 

 such is the case is sustained by considerable collateral evidence, 

 first of which is the invulnerability of the haemoglobin mole- 

 cule. 



Paradoxical as this statement appears, it nevertheless con- 

 stitutes the key-stone of the entire edifice, since it is only when 

 vulnerable that the molecule becomes the prey of disintegrating 

 influences. We have used the words "reducing agents" several 

 times; but the hemoglobin molecule does not yield to even 

 moderately-strong reagents of this nature; indeed, only a 

 powerful agent sulphuric acid, for instance will dissociate 

 it: an exemplification of the wonderful binding power which 

 the suprarenal secretion must exert upon all its constituent 

 parts. Still, we must not overlook the fact that the oxidizing 

 substance in the blood-plasma is identical to this binding com- 

 pound. Indeed, we have accumulated so much testimony 

 affirming the fact that the plasma per se is a potent source of 

 energy, while the red corpuscles always played so secondary a 

 role in the various intrinsic functional mechanisms, especially 

 those concerned with muscular and glandular elements, that 

 we have been led to conclude that the red disks are, after all, 

 but servants of the blood-plasma: pack-mules, as it were, from 

 which it can draw, as needed, enough oxidizing substance to 

 maintain its own functional potentiality as previously stated. 



Under these circumstances we can readily see how the 

 haemoglobin molecule, gradually deprived of its binding oxidiz- 

 ing substance during the inordinate metabolism which the tis- 

 sues of the digestive organs undergo during their periods of 

 activity, should yield more readily to dissociating influences. 

 It is evident that a molecule so weakened, thrust in blood 

 such as that of the portal vein, a vast sewer replete with 

 physiological waste-products and deoxidized blood-cells, all 

 bathing in a plasma itself despoiled of its oxidizing substance, 

 should soon become dissociated. Transported through grad- 

 ually narrowing channels, the walls of which, like all tissues, 

 eagerly absorb any loose oxygen that it may contain, it must 

 inevitably undergo the transformation of haemoglobin referred 



