306 THE GROWTH OF THE BRAIN. 



nervous system, and the question takes the form 

 whether the nervous elements can discharge without 

 being immediately excited by incoming stimuli. 



The test would be found in the reactions of these 

 cells when deprived of all such stimuli. As a result 

 of attempts to do this it is discovered that when the 

 stimuli can really be removed the reactions cease, and 

 that the nonconforming cases are those in which the 

 stimuli cannot be controlled. As applied to the move- 

 ments of the entire animal the view that automatic 

 reactions are but a series of responses to stimuli more 

 or less masked, may be illustrated in the following way : 

 If a frog be deprived of its brain (encephalon), the cord 

 being left intact, it will remain irritable for several days. 

 Such a frog exhibits no automatic movements. It 

 remains where it is placed. If the skin is stimulated, 

 it reacts by a contraction of the appropriate muscles, 

 and the reaction being completed, relapses into the 

 quiescent state. The force and extent of the reaction in 

 such a case is predictable since it depends in a large 

 measure on the character of the stimulus. Let such 

 a frog be compared with others in which successively 

 smaller portions of the brain have been removed. As the 

 quantity removed becomes less there is an increase in 

 the number of the sense organs remaining intact, together 

 with an increase of the total mass of nervous centres. 

 The less the quantity removed the less predictable 

 become the reactions of the frog, and the more difficult 

 is the correlation between them and the stimulus, 

 because for one thing there are greater variations in the 

 excitability of the nerve centres themselves. But at 

 best a normal frog is not a very complicated affair. It 

 can safely be said that when pursued it will try to escape, 

 though just how many jumps it will make and in what 

 direction it will go are uncertain. If, passing up the 



