842 THE CENTRAL NERVOUS SYSTEM 



From these results it is in general clear that the brain stem is able 

 to adjust the motor and the visceral reactions of the animal to changes 

 in the immediate environment, but that no power of spontaneous move- 

 ment is possible. Although in the higher apes and in man removal of 

 any considerable part of the cerebral cortex is impossible, yet we may 

 infer, from the results which have just been considered, that in the 

 higher animals more and more of the action becomes shifted to the 

 motor centers of the cerebrum. Reflexes which in the lower animals 

 involve only a spinal or a bulbo-spinal tract, also involve in the higher 

 forms a cerebral path which is laid down only as the result of experience 

 and education. The newly born infant is able to perform fewer move- 

 ments than is the case in the lower forms of animal life, but his power 

 of learning new movements is incomparably greater. He inherits less 

 in the way of stereotyped reflexes, but in place of these he possesses 

 innumerable nerve tracts leading through cerebral neurons, through 

 which new reflex responses may be laid down as a result of education. 



In connection with these experiments it is interesting to note that 

 in lower animals it can readily be demonstrated that the general in- 

 fluence of the higher on the spinal centers is of an inhibitory nature. 

 Thus, the latent time of the flexion reflex in the decerebrate frog, as 

 judged by the Turck method,* is very much prolonged when a stimulus, 

 such as that produced by a crystal of common salt, is applied to the 

 optic lobes just posterior to the cerebrum. In general, the influence 

 which the cerebrum exercises on the spinal centers is an inhibitory one, 

 whereas that of the cerebellum is augmentatory. 



*Turck's method consists in measuring with a metronome the time that eJapses between dipping 

 the foot into weak acid solution and the reflex flexion of the leg. 



