INTRODUCTORY 1 1 



by sucking, the adjustment is beneficial ; although the infant does 

 not, as a matter of fact, obtain any milk at first, and although a 

 finger or a rubber nipple on an empty bottle, or any other object 

 of suitable size and texture, in the mouth of a hungry infant, 

 excites the nerves and muscles so as to call forth the act of suck- 

 ing, and, so far, to satisfy the calls of nature. 



Preyer says "when I put into the mouth of the screaming 

 child, whose head alone was as yet born, the ivory pencil or a 

 finger, the child began to suck, opened its eyes, and seemed, to 

 judge from its countenance, to be most agreeably affected. In 

 the case of another child, which cried out immediately after its 

 head emerged from the womb, I put my finger, three minutes 

 later, into the child's mouth, and pressed it on the tongue. At 

 once all crying ceased, a brisk sucking began, and the expression 

 of the countenance, which had been hitherto discontented, became 

 suddenly altered. The child, not yet fully born, seemed to expe- 

 rience something agreeable, and therewith — during the sucking 

 of the finger — the eyes were widely opened." 



•Although changes which are directly due to nature do not 

 take place without a stimulus, they do take place mechanically, 

 or independently of experience, under the natural stimulus, or 

 under any other which is applied in the same way. The blow- 

 fly, which is stimulated by the odor of putrid flesh to lay its eggs 

 where the larvae will find abundant food, sometimes lays them on 

 the stinking arum, misled by its odor. In this case the deceptive 

 stimulus resembles the normal one in certain sensible qualities, 

 but it is most important, for reasons which will be given later, 

 to note that the natural responses of living things may be called 

 forth by any stimulus which is similar in its mode of application 

 to the normal or natural stimulus, whether it is or is not similar 

 in any sensible properties except those which act as the stimulus. 

 The finger, which feels like a nipple, stimulates the infant and 

 calls out the sucking response, but electrical stimulation of the 

 lips and tongue, if applied with sufficient skill, might give the 

 same result, although this does not resemble the nipple in any 

 sensible qualities except the ones which effect the stimulation. 



In the order of nature each stimulus is a sign with a signifi- 

 cance, and our own reason, which consciously apprehends the 



