IV 



REFLEX ACTION 47 



these remain uninterrupted, rotate it will. Similarly the 

 sucking reflex is well adapted to the needs of babies and 

 other young animals for food, but it is a response not to 

 the nipple nor to the food, but to anything that comes into 

 the lips. 1 Hence the infant in its leisure moments sucks 

 its thumb or anything else that comes handy. /** 



What has been said is perhaps sufficient to show that, 

 speaking generally, the reflex is determined by the struc- 

 ture, or a portion of the structure, of the organism which 

 is specially arranged to meet a specific sensory stimulus 

 with a specific reaction. It is easy to see, first, that such 

 a type of action can readily be conceived of as arising 

 under the influence of natural selection, where, under 

 ordinary circumstances, one sort of reaction, A, to a 

 stimulus a, is decidedly more often beneficial than any 

 other. It will also be seen that a mode of action so 

 arising will, in a preponderant number of cases, but not 

 necessarily in all, be suited to the actual needs of the 

 individual in a given case. While, lastly, such an action 

 would not imply on the part of the individual any sort 

 of intelligent purpose in the sense of a power to remodel 

 its behaviour at need in such a way as to bring about a 

 result to which it looks forward. 



6. Uniform reaction to present stimulus is the charac- 

 teristic of unintelligent response in general. But given 

 such response, there are still two possibilities. It may de- 

 pend on the condition of the organism as a whole, and if 

 so, the normal reaction to one stimulus may be modified 

 by the effect of other simultaneous stimuli, internal and 

 external. Or it may be a response of a definite part of 

 the bodily structure assigned to one particular element in 



1 Preyer, I. p. 127. "Experiments on little guinea-pigs, only eight to 

 sixteen hours old, and separated from the mother after two hours, proved 

 to me absolutely that concentrated water-solutions of tartaric acid, soda, 

 glycerine, introduced into the mouth through glass tubes, are swallowed 

 just as greedily or eagerly as cow's milk and water, with vigorous 

 sucking. But then the empty tube, placed with the end upon the tongue, 

 occasioned just such sucking. The experiments conducted in this 

 manner cannot, therefore, yield much that can be depended upon. 

 Touch, as a reflex stimulus to sucking in hungry new-born creatures, 

 overpowers any taste-stimuli acting at the same time. Newly-born 

 animals that have eaten enough do not, however, suck regularly in 

 general." For human infants, see p. no. 



