308 DEVELOPMENT AND PURPOSE CHAP. 



question has now to be asked whether this interdependence 

 may not, after all, be conceived in mechanical terms. May 

 we not, that is to say, contemplate an arrangement, call it 

 of organs, cells, molecules, or, if preferred, of forces such 

 as (a) in response to normal stimuli will run a certain pre- 

 scribed course, as a wound clock gradually runs down 

 marking the hours the while, and (b) by special and highly 

 intricate combinations will provide, within limits, for certain 

 deviations from the normal. The nature of the provision 

 may be set forth in this wise. Let us imagine elements 

 A, B, C . . . functioning normally along lines which we may 

 distinguish as Aa, B/3, Gy. Then it must be prearranged 

 that a change a' affecting A produces a corresponding change 

 /3' in B, and this again produces 7' in C. The system Aa', 

 B/3', Cy', we must suppose, will ' work,' that is, it will be 

 able to maintain itself as a system just as the normal Aa, 

 B/3, C-y, can do. The simplest case, in fact, will be that in 

 which the effect /3' is such as to react upon a and tend to 

 reduce its divagation from the standard a. This is the 

 case, for example, with the repair of tissue or with the 

 adjustment of the balance of oxidation in the example 

 which we took. Somewhat more complex but still intelli- 

 gible enough is the case where the organic structure is in 

 some measure modified, but without losing its recognisable 

 identity or interrupting its life process. In this case $ 

 and y do not tend to neutralise a', but rather to complement 

 it. They are the modifications in /3 and 7 required by 

 the change in a in order to maintain the moving equili- 

 brium. This is the case of the broken bone set crooked, 

 which, to maintain its function as a whole, modifies the lie 

 of its component parts so as to meet the new lines of strain. 

 Some such compensatory arrangements are undoubtedly 

 observable in machines. The 'governor' of a common 

 steam engine, for example, is a device whereby excess of 

 speed, due to a sudden diminution of resistance, corrects 

 itself by closing the throttle valve and diminishing the 

 supply of steam. The c compensating pendulum ' main- 

 tains the resultant length of the pendulum unaffected or 

 almost unaffected by changes of temperature. The very 

 change which disturbs the balance in one direction is made 



