148 THE PHILOSOPHY OF BIOLOGY 



as a protest against the anthropomorphism which saw 

 in the flying of a moth into a flame the expression of 

 an emotion ; or in the movements of a caterpillar on a 

 green shrub the expression of hunger and satiety and 

 of the inherited experience of the animal ; or in the 

 avoidance by a Paramcecium of a drop of acid the 

 emotion of dislike of the feeling of pain. Well, let it 

 be granted that this is so, and that the protest was a 

 useful one, for it is obviously impossible that these 

 notions as to the causes of the movements can be 

 verified : does it improve matters to take refuge in 

 an hypothesis which is just as purely physico-chemical 

 dogmatism as the other is anthropomorphism ? But 

 the former hypothesis is at all events one which is 

 susceptible of experimental verification and in this lies 

 its usefulness, inasmuch as it has stimulated investiga- 

 tion. It is evident, however, that this verification 

 has not yet been made. The differential afferent 

 impulses set up by the energy-field ; the increases or 

 inhibition of muscular tone ; the presence of photo- 

 sensitive substances in the tissues of tactically acting 

 lower animals ; the change of velocity of chemical 

 reaction, in these cases, which ought to follow stimula- 

 tion — all these things could be verified if they possess 

 reality. Yet it is only indirect proofs, capable perhaps 

 of other interpretations, and not direct experimental 

 ones, which have so far been adduced in favour of a 

 general theory of tropisms. 



Moreover, the close analysis of the actions of some 

 of the lower organisms by Jennings has shown that 

 the tactic hypothesis is probably false in the majority 

 of cases. This observer studied the acting of the 

 organisms themselves and not the beginning and end 

 of the series, and he shows that the behaviour of the 

 organisms is far more obviously described by saying 



