150 ANIMAL BEHAVIOUR 



becomes less elastic, a thermionic valve '' loses its emission," 

 and so on, but the proper analogy with these phenomena are 

 the '' senile decay," or the bodily accidents of an animal and 

 not the changes in its modes of behaviour. The changes under- 

 gone by the physical systems are manifestations of the physical 

 and chemical degradations expressed by the entropy law and 

 they tend to the loss of the particular " properties " of the 

 systems. On the other hand, the experience of an animal tends 

 to make its behaviour more efficient and purposeful — that is, the 

 better to satisfy the needs and desires implied in the urges of 

 life. 



Causality a?id experience. The causality included in a physical 

 system is measured by the quantity of available energy, but 

 this need not be the case when the system includes an organism. 

 Thus CO 2, OH 2 and some other simple mineral substances, with 

 solar radiation make up a system in which the available energy 

 (or sunlight) simply dissipates. But let the system include a 

 green plant and carbohydrate is formed, when available energy, 

 or causality, is conserved. The system may be CO 2, OH 2, etc., 

 with the energy from a quartz mercury- vapour lamp, glass 

 vessels and an experimental chemist. Such systems existed in 

 the nineteenth century, but they did not synthesize carbohydrate. 

 But at the present time chemists " of experience " can so assemble 

 the apparatus as to couple together energy-transformations and 

 bring about the syntheses. The latter are still very imperfect — 

 that is, the " yield " of sugar in any experiment is small, but 

 we have no doubt that additional *' experience " will tend to 

 increase this " yield." Thus there is physical causality measur- 

 able by the available energy of the system considered and there 

 is also organic causality which is inherent in the behaviour of 

 some animal which is associated with physical things. This 

 causality, or skill, or efficiency of behaviour is not diminished 

 by use and it can be communicated without diminution. It 

 increases by individual acquirement — thus all good artisans, 

 surgeons, etc., become more skilful, that is, become centres of 

 increased causality. This increase of causality, due to their 

 greater power over the things in their environment, is their organic 

 experience . 



The *' Retention of the past.'' The past is said (in a loose 

 kind of way) to " survive," or partially to be retained in an 



