18 PSYCHOLOGY. 



selves we should Ciill an idea. His reactions to outward 

 stimuli vary their form, too. Instead of making simple 

 defensive movements with his hind legs like a headless 

 frog if touched, or of giving one or two leaps and then sit- 

 ting still like a hemisphereless one, he makes persistent 

 and varied efforts at escape, as if, not the mere contact of 

 the physiologist's hand, but the notion of danger suggested 

 by it were now his spur. Led by the feeling of hunger, 

 too, he goes in search of insects, fish, or smaller frogs, and 

 varies his procedure with each species of victim. The 

 physiologist cannot by manipulating him elicit croaking, 

 crawling up a board, swimming or stopping, at will. His 

 conduct has become incalculable. We can no longer foretell 

 it exactly. Effort to escape is his dominant reaction, but 

 he may do anything else, even swell up and become per- 

 fectly passive in our hands. 



Such are the phenomena commonly observed, and such 

 the impressions which one naturally receives. Certain 

 general conclusions follow irresistibly. First of all the 

 following : 



The acts of all the centres involve the use of the same 

 muscles. "When a headless frog's hind leg wipes the acid, he 

 calls into play all the leg-muscles which a frog with his 

 full medulla oblongata and cerebellum uses when he turns 

 from his back to his belh'. Their contractions are, how- 

 ever, combined differently in the two cases, so that the re- 

 sults vary widely. We must consequently conclude that 

 S23ecific arrangements of cells and fibres exist in the 

 cord for wiping, in the medulla for turning over, etc. 

 Similarly they exist in the thalami for jumping over 

 seen obstacles and for balancing the moved body ; in the 

 optic lobes for creeping backwards, or what not. But in 

 the hemispheres, since the presence of these organs brings 

 no neiv elementary form of movement with it, but only deter- 

 mines differently the occasions on which the movements shall 

 occur, making the usual stimuli less fatal and machine-like ; 

 we need suppose no such machinery directly co-ordinative 

 of muscular contractions to exist. We may rather assume, 

 when the mandate for a wiping-movement is sent forth by 



