ANIMAL AUTOMATISM. 235 



without a grimace, a tumbler of strong vinegar and water 

 which was put into his hand. 



An experiment which may be performed upon the 

 frog deprived of the fore part of its brain, well known 

 as Goltz's " Quak-versuch," affords a parallel to this per- 

 formance. If the skin of a certain part of the back of 

 such a frog is gently stroked with the finger, it imme- 

 diately croaks. It never croaks unless it is so stroked, 

 and the croak always follows the stroke, just as the 

 sound of a repeater follows the touching of the spring. 

 In the frog, this " song " is innate so to speak d priori 

 and depends upon a mechanism in the brain governing 

 the vocal apparatus, which is set at work by the mo- 

 lecular change set up in the sensory nerves of the skin 

 of the back by the contact of a foreign body. 



In man there is also a vocal mechanism, and the cry 

 of an infant is in the same sense innate and d priori, 

 inasmuch as it depends on an organic relation between 

 its sensory nerves and the nervous mechanism which 

 governs the vocal apparatus. Learning to speak, and 

 learning to sing, are processes by which the vocal mech- 

 anism is set to new tunes. A song which has been 

 learned has its molecular equivalent, which potentially 

 represents it in the brain, just as a musical box wound 

 up potentially represents an overture. Touch the stop 

 and the overture begins ; send a molecular impulse along 

 the proper afferent nerve and the singer begins his song. 



Again, the manner in which the frog, though appar- 

 ently insensible to light, is yet, under some circumstances, 



