336 THE ADRENAL, GENERAL MOTOR, AND VAGAL SYSTEMS. 



a haemochromogen is formed which slowly loses its iron, the 

 end-product being also haematoporphyrin. 



It is evident that the integrity of the haemoglobin mole- 

 cule is dependent upon the quantity of secretion that the ad- 

 renals supply to the blood, and also upon the condition of that 

 molecule at a given time. In other words, while the adrenals 

 may be supplying their normal proportion of secretion, the 

 haemoglobin molecule in the red corpuscles of venous blood 

 i.e., blood about to return to the vena cava for a fresh sup- 

 ply may be compared to that of blood during insufficiency. 

 Even as haemoglobin, the blood-pigment is loosely combined; 

 when approaching the end of its systemic circle, it is still 

 nearer the state of disintegration according to the activity of 

 the oxidation processes which it has subserved. Starting from 

 the lungs as oxyhaemoglobin, it may return to the heart as 

 haemoglobin or reduced haemoglobin, ready to at once absorb 

 another supply of suprarenal secretion and, once in the lungs, 

 take up its oxygen. 



Blood from the head, extremities, and other structures in 

 which the drain upon its resources has not been excessive, re- 

 turns such a molecule to the heart; it is still efficient as an 

 oxygen-carrier. But not so with the blood from any organ directly 

 connected with the digestive system. As is well known, all the 

 blood from the organs of the alimentary tract stomach, intes- 

 tine, pancreas, and spleen is not returned to the heart before 

 it has been submitted to whatever action the liver may have 

 upon it; then only can it re-enter the circulation through the 

 hepatic veins, which carry the blood to the vena cava. But not 

 all the blood may thus be rejuvenated; some has gone beyond; 

 it has, indeed, almost reached the state of haematoporphyrin, 

 the last on the list of pigments, that which appears in the most 

 advanced stages of suprarenal insufficiency. We have seen 

 that haematoporphyrin and bilirubin are similar; and, as is 

 well known, it is bilirubin which passes out with the bile. 



A salient feature of the haemoglobin molecule is missing 

 here, however, namely: the iron. As stated, a reducing agent, 

 if used in the presence of oxygen, will reduce haemoglobin in 

 the absence of oxygen; the primary product is a haemochro- 

 mogen which gradually parts with its iron, leaving as end- 



