148 ANIMAL BEHAVIOUR 



nothing " with a reflex. There is a stimulus of a certain minimal 

 intensity and if below this intensity it will not lead to effect. 

 If it has effect it is the full effect. There are gradations of 

 strength in, say, the muscular act that follows a stimulus, but 

 these are consequent on more or few^er of the fibres in the nerve, 

 or muscle, being stimulated. (3) There is a '* refractory period " 

 following the stimulation of a nerve and during this another 

 stimulus does not act. (4) There is " fatigue " in the reflex, 

 but this is in the synapses, or in the substances adjacent to the 

 end-organs in the muscles. (5) There are " facilitation " and 

 " induction " in reflexes, that is, one stimulus may reinforce 

 another one and one subliminal stimulus following another in 

 the same field of receptors may have effect. (6) There is 

 " exaltation " of effect following an inhibition of a reflex. (7) 

 The effect of stimulating a nerve depends on the ending of the 

 nerve in the effector organ. And so on. 



Chained Reflexes. In the intact animal there are chains of 

 reflexes, the effect of one being the stimulus for the next, and 

 so on. Thus the successive contractions of the oesophagus in 

 swallowing ; the writhing locomotion of the foot of a snail, or 

 the successive action of the segments of an earthworm, etc., 

 or the stimulus of seeing a fly causes the frog to dart out its 

 tongue and catch the insect, when contact of the latter with 

 the mucous membrane of the mouth causes the latter to close, 

 which is the stimulus for the swallowing movements of the 

 gullet. 



Combining of reflexes. Thus antagonistic muscles are stimu- 

 lated in succession, or the stimulus to contraction of the muscle 

 that bends a limb is simultaneous with the stimulus to relaxation 

 of the antagonistic muscle that straightens the same hmb. And 

 in complex activities the reflexes are initiated and co-ordinated 

 in ways that are beyond analysis except in simple cases. 



And it will easily be seen that all the mechanism indicated 

 in the above sections do not, in the least, explain behaviour : 

 they are only analyses of the means of behaviour. How activities 

 are adjusted to the circumstances is our problem, and it is 

 obviously a psychical one. 



53^. The Purposes of Reflexes. Just as easily do we see 

 that all the reflexes that can be studied have purpose, in the 

 sense of the term adopted. The scratch reflex of the dog is 



