138 . THE NEW PHYSIOLOGY. 



The conception of a living organism as a mechanism is 

 in some respects quite natural and very useful. We 

 can, for instance, understand up to a certain point the 

 movements of the limbs if we regard the bones as levers 

 acted on by the contractions of the muscles. It is equally 

 natural to seek for corresponding mechanical explanation 

 of the contraction of muscle ; and though definite pro- 

 gress in this direction has hitherto been limited, I feel 

 confident that we are on the eve of such progress. When 

 we turn to any other form of bodily activity we find 

 similarly that physical and chemical explanations will 

 carry us a long step forwards. Thus the chemistry of 

 the blood enables us to see exactly how oxygen is carried 

 from the lungs to the tissues, and carbon dioxide is 

 carried from the tissues to the lungs : the chemistry of 

 the digestive secretions enables us to understand the 

 chemical changes in digestion ; and the structure of the 

 eye and the laws of optics show us how an image is 

 formed on the retina. At first sight, therefore, it seems 

 justifiable to assume that if our knowledge of the chem- 

 istry and physics of the living body were sufficiently 

 complete, we could explain completely all the phenomena 

 occurring in living organisms. 



It used often to be stated confidently that the develop- 

 ment of physiology shows a continuous advance towards 

 a mechanical explanation of life ; and this statement is 

 at present widely accepted. It is certainly true that 

 physical and chemical explanations are being profitably 

 applied to more and more of the phenomena associated 

 with life. It is, however, equally true that more and 

 more of these phenomena are being found to be quite 

 insusceptible of the simple mechanical explanations 



