THE PRESIDENTIAL ADDRESS. 



SOME ASPECTS OF ANIMAL 

 MECHANISM. 



BY 



Professor Sir C. S. SHEREINGTON, G.B.E., ScD., D.Sc, 



LL.D., Pres.E.S., 



PRESIDENT OF THE ASSOCIATION. 



It is sometimes said that Science lives too much to itself. Once a 

 year it tries to remove that reproach. The British Association meeting 

 is that annual occasion, with its opportunity of talking in wider gather- 

 ings about scientific questions and findings. Often the answers are 

 tentative. Commonly questions most difficult are those that can be 

 quite briefly put. Thus, ' Is the living organism a machine?' 'Is 

 life the running of a mechanism? ' The answer cannot certainly be 

 as short as the question. But let us, in the hour before us, examine 

 some of the points it raises. 



Of course for us the problem is not the why of the living organism 

 but the how of its working. If we put before ourselves some aspects 

 of this working we may judge for ourselves some at least of the 

 contents of the question. It might be thought that the problem is 

 presented at its simplest in the simplest forms of life. Yet it is in 

 certain aspects more seizable in complex animals than it is in simpler 

 forms. And so let us turn thither. 



Our own body is full of exquisite mechanism. Many exemplifica- 

 tions could be chosen. There is the mechanism by which the general 

 complex internal medium, the blood, is kept relatively constant in its 

 chemical reaction, despite the variety of the food replenishing it and 

 the fluctuating draft from and input into it from various organs and 

 tissues. In this mechanism the kidney cells and the lung cells form 

 two of the main sub-mechanisms. And one part of the latter is the 

 delicate meclianism linking the condition of the air at the bottom of 

 tliG lungs with tliat particular part of the nervous system which manages 

 the ventilation of the lungs. On that ventilation depends the proper 

 respiratory condition of the blood. The nervous centre which manages 

 the rhythmic breathing of the chest is so responsive to the respiratory 



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