126 THE ADRENALS AND THE RESPIRATORY BLOOD-CHANGES. 



and since these constituents tend to fall apart when the secre- 

 tion fails them, its flow into the circulation must ~be continuous. 

 Again, we know that venous blood contains not only reduced 

 haemoglobin, but a considerable proportion of oxyhaemoglobin. 

 The red corpuscles must therefore always be supplied with 

 more oxygen than the tissues utilize: a fact which warrants 

 the conclusion that even reduced haemoglobin, under normal 

 conditions, is always sufficiently supplied with this gas to 

 preserve its integrity as a unit. But this conclusion in itself 

 testifies to the presence in the hcemoglobin-molecule of suprarenal 

 secretion, and therefore to the fact that, as long as its integrity 

 is preserved, it is capable of taking up an equivalent of oxygen 

 in the lungs. 



This does not modify, however, the present teachings of 

 physiology as regards the role of the blood-pigment in the 

 circulation. "Undergoing no intrinsic change in itself/ 7 writes 

 Foster, "the haemoglobin combines in the lungs with the 

 oxygen which it carries to the tissues; these, more greedy of 

 oxygen than itself, rob it of its charge, and the reduced haemo- 

 globin hurries back to the lungs in the venous blood for an- 

 other portion." 



That gaseous diffusion and endosmosis are unimportant 

 factors of the respiratory process seems probable in view of 

 the foregoing facts. "Whenever oxygen is mixed with venous 

 blood, even in vitro during experiments, the carbonic acid 

 is immediately given off" writes Mathias Duval. "One' is 

 led to admit, therefore, that the combination of oxygen with 

 the blood-corpuscle (oxyhaemoglobin) plays a role analogous 

 to that of an acid and involving the elimination of carbonic 

 acid from venous blood." The potent agency underlying the 

 affinity of the blood-pigment for oxygen, we have seen, simu- 

 lates an acid in its effects. The elimination of carbonic acid, 

 therefore, includes the physical expulsion of a gas for which 

 the haemoglobin itself, when normally supplied with the supra- 

 renal secretion, has less affinity than it has for oxygen. In 

 carbonic-acid poisoning suprarenal insufficiency prevails, as it 

 does in the case of poisons and venoms reviewed in this con- 

 nection. Blood studied outside the body is, therefore, but an 

 approximate and variable criterion of the physiological func- 



