102 ORGANISM AND ENVIRONMENT 



dioxide in the alveolar air, we first test it under vary- 

 ing conditions so as to make sure of its relative 

 stability, and then proceed to investigate its connection 

 with and subordination to other normals. Thus we 

 find that the normal concentration of carbon dioxide 

 in the alveolar air is connected with or subordinate to 

 the normal composition of the blood, the normal 

 activity of the respiratory centre, heart, kidneys, and 

 other organs, the normal composition and amount of 

 the food and the normal concentration of oxygen in 

 the air. Our general working hypothesis would have 

 told in a general way that connections of this kind 

 must exist; but special investigation could alone tell 

 us how they exist and how one is directly subordinate 

 to another. It is this kind of investigation that is 

 experimental physiology. The normals of anatomy 

 are not mere physical structure, nor are the normals of 

 physiology mere averages : they are manifestations of 

 the life of an organism regarded as a whole. We 

 have seen, for instance, in the case of the alveolar 

 carbon dioxide pressure, in the percentage of haemo- 

 globin in the blood, in the structure of bone-marrow, 

 how a subordinate normal alters as the organism 

 adapts itself so as to preserve its more fundamental 

 normals under new conditions. In pathological condi- 

 tions we find remarkable alterations in subordinate 

 normals, and these alterations are undoubtedly the 

 expression, to a large extent, of adaptations to the 

 altered conditions. Pathological phenomena are not 

 mere chance effects of the environment on the organ- 



