128 THE ADRENALS AND THE RESPIRATORY BLOOD-CHANGES. 



1. The adrenals secrete a chromogen a colloid, hyaline fluid 

 which leaves the organs through the suprarenal veins, and is 

 mixed with the plasma of the venous blood in the inferior vena 

 cava. 



2. When the venous Nood reaches the pulmonary alveoli, the 

 marked affinity of the adrenalized plasma for oxygen causes it to 

 absorb this gas from the alveolar air. 



3. The carbonic dioxide in the blood is thus forcibly replaced 

 by oxygen, and expelled with corresponding vigor. 



4- The red corpuscles, after this operation, bathe in an oxygen- 

 laden medium, and their haemoglobin becomes reconverted into oxy- 

 hcemoglobin. 



The mechanism of respiration, and the manner in which 

 the adrenal secretion and the air are brought into contact in 

 the alveolar elements will be studied in a subsequent chapter. 



As regards the relations between this process and the 

 preservation or dissociation of haemoglobin, the following deduc- 

 tions seem warranted: 



1. The periodical exposure of the hcemoglobin-molecule to the 

 oxygen-laden adrenal secretion in the lungs serves to keep its con- 

 stituents associated." 



2. Deficiency, quantitative or qualitative, of adrenal secre- 

 tion by reducing the oxygen-absorbing power of the plasma corre- 

 spondingly reduces the mutual affinity of the hcemoglobin constit- 

 uents. 



3. When the molecular combination of the hcemoglobin constit- 

 uents becomes sufficiently loose from this cause, portions of the 

 hcemoglobin are detached and follow the arterial blood-stream in 

 their reduced state, and the efficiency of the blood is reduced in 

 proportion. 



4. The physiological absorption of oxygen by the tissues not 

 only reduces the oxyhcemoglobin, but further dissociates this ad- 

 ventitious haemoglobin into its component bodies. 



5. The component bodies of haemoglobin thus dissociated are: 



(a) Methcemofjlobin or its isomer, hcematin (C 32 H 34 FeN 4 6 ). 



(b) Hcematoporphyrin or its isomers, iron-free hcsmatin, 

 hcemato'idin, and bilirubin (C 32 H 36 N 4 6 ). 



(c) HcBmatoporphyrin (usually termed hcemato'idin) appears 

 in the blood when the adrenals are removed or when their functions 



