324 THE PHILOSOPHY OF BIOLOGY 



must vary in length, being sometimes closer together, 

 sometimes further apart. The mean step has a definite 

 length and requires the expenditure of a certain amount 

 of energy, and the condition that the man takes some- 

 times a long step and sometimes a short one does not 

 require that the energy expended on the steps should 

 be more than if every one of them were of the mean 

 length, for the additional energy that is required for 

 the long steps is saved from the short ones. That 

 which operates here is the power of regulation exercised 

 by the walker regarded as a mechanism. There is no 

 purely inorganic process precisely similar to this. It 

 might be thought that the governor of a steam engine 

 did very much the same thing, admitting more steam 

 into the cylinder when the load on the engine increases, 

 and vice versa. But the governor is a mechanism 

 designed to compensate for variations that are given in 

 advance. In the case of the man walking on the rail- 

 way track, entelechy operates by suspending energetic 

 happening (the muscular contractions of the short 

 steps) when necessary, and allowing it to proceed when 

 necessary. Entelechy itself, whatever it may be, need 

 not be affected by these regulations. 



The organism is therefore an aggregation of chemi- 

 cal substances arranged in a typical manner. These 

 substances possess energy in the potential form, capable 

 of undergoing transformation so that they may give 

 rise to other chemical substances — secretions, for 

 instance — or to energy in the kinetic form, that is, the 

 movements of muscles. In the resting organism these 

 transformations do not take place : the energy remains 

 potential, so that chemical happening is suspended. In 

 the unfertilised ovum, for instance, nothing happens 

 although all the potentialities of segmentation are 

 contained in the cell. If reactions did occur in con- 



