58 MIND IN EVOLUTION CHAP. 



effort is its own tendency to produce a result other than 

 itself, and this conforms to our general definition of 

 conation and distinguishes it from reflex action, in which, 

 as in everything mechanical, the result is indifferent. 



The simplest form of conation then seems to be action 

 directed vaguely to a change of conditions, persisted in or 

 varied until new and more suitable conditions are obtained. 

 Such action is not purpose because it does not clearly 

 foresee these conditions, but it is conation because it is 

 determined by the contrast between the existing state of 

 the organism and the relief which in fact it tends to bring 

 about. Conation at this stage is found to all appearance 

 among unicellular organisms. Thus Paramecium, in 

 normal conditions, swims gently forward, absorbing food 

 by whirling its cilia. If it encounters a solid body it backs 

 a little, then swings round through an angle of varying 

 magnitude and advances again. If again it strikes the 

 object, the process is repeated and various directions are 

 tried, so that in the end, if there is any egress, it is found. 

 The animal seems in a fashion to explore the object, but 

 the exploration is indirect and persists through the inhi- 

 bition of repeated errors. Paramecia will behave in the 

 same way to a drop of many chemical solutions. It swims 

 up to the edge of the drop if not too strong, and then 

 reacts in the way described, so that, seen through the 

 microscope, the drop remains empty, while the weaker 

 solution around is crowded with Paramecia. This occurs 

 when the reaction to the drop is what is called negative. 

 The converse case has a special interest. When a drop of 

 weaker solution is contained in one of a stronger the 

 Paramecia appear to be positively attracted to it, and 

 superficially it looks as though they swam deliberately to 

 the spot preferred, which is soon crowded with Paramecia, 

 while the rest of the liquid is empty. But in reality the 

 result is only reached by an indirect method and the 

 continued repetition of the negative reaction. The organ- 

 ism swims at random, but any individual which enters the 

 drop proceeds across it until it reaches the edge of the 

 stronger solution. There it gives the avoiding reaction 

 and starts off swimming in a new direction till it reaches 



