104 ORGANISM AND ENVIRONMENT 



organic activity. The oxygen which passes into the 

 lungs is just ordinary oxygen, driven inwards to the 

 alveoli by an ordinary atmospheric pressure difference. 

 The process is organically regulated, but the regulation 

 appears to be something external to the oxygen, which 

 still retains its usual properties. We can then trace 

 its diffusion into the blood, its combination with haemo- 

 globin, its carriage onwards by the pumping action 

 of the heart, and its dissociation from the haemoglobin 

 in the systemic capillaries. It has come under more 

 intimate organic control in the blood, but we can still 

 trace it as molecules of ordinary oxygen. When it 

 reaches and is absorbed by the tissues in cell metabol- 

 ism the organic control becomes far more intimate. 

 It is caught up in a whirl in which its behaviour is 

 from the physical and chemical standpoint utterly mys- 

 terious. We can imagine no form of chemical com- 

 bination which will now explain the behaviour of the 

 oxygen. The mental picture of oxygen atoms or mole- 

 cules seems to fade away, and to be replaced by an- 

 other picture in which organisation is not something 

 external to organised material, but is absolutely iden- 

 tical with the material, so that both the material 

 and its movements are nothing but manifestations of 

 the organisation. It is life and not matter which we 

 have before us. 



We can endeavour to hold on to the physical and 

 chemical picture, and to seek for substances in the 

 living structure which combine with, or enter into 

 other physical or chemical relations with the oxygen. 

 But a little consideration shows that even if we find 



