LOCALIZATION OF FUNCTION IN THE NERVOUS SYSTEM 121 



" Intelligence," which is a very vague expression for something 

 almost intangible, is dependent upon the degree of development of 

 the cerebral cortex and especially upon the neurones of the asso- 

 ciation areas. The ability of an animal to profit by experience, 

 which involves analj'sis of a situation and memory, and which 

 enables the individual to react in a way that is advantageous in a 

 new situation, is determined by its degree of intelligence. This, in 

 turn, is limited by the number of adjustor neurones and the 

 synapses possible between them. It is well known that all the 

 neurones that an animal possesses are present at a very early stage 

 of its development. New synapses are, however, formed through- 

 out the life of the individual and probably depend upon the variety 

 and intensity of the stimuU received by that individual. For 

 example, it has been found that if light be prevented from stimu- 

 lating the eyes of an animal, such as a dog, the adjustor neurones 

 in the optic lobes do not grow and send out processes in the usual 

 manner (Fig. 66). The sensory impulses that reach the cerebrum 

 the motor impulses that pass out from it, and the associations made 

 in it constitute our so-called " consciousness." Sleep and anaes- 

 thetics in some way lessen or completely block the functioning of 

 the cortex and produce unconsciousness. It is sometimes said that 

 the cortex " initiates " or controls " voluntary " movements. 

 While there is no necessity of entering upon a discussion of the 

 " will," it must be remarked that, so far as the physiology of the 

 nervous system is understood, the motor centers of the cerebrum 

 transmit impulses produced by stinuili, just as do other parts of 

 the central system. The sources of the stimuli may be difficult to 

 locate, but that does not seem to be a sufficient reason for depart- 

 ing from the neurone mechanism as an explanation. 



In order to make clear the functions of the nervous system, 

 the analogy to a telephone system is sometimes employed. The 

 various lines that place individual telephones in connection with 

 one another would correspond roughly to the peripheral system. 

 " Central " occupies a position similar to the central nervous sys- 

 tem. If we had in our telephone system certain hnes that con- 

 nected one central office with another central office, these would 

 correspond to the adjustor neurones. 



It is also possible to compare the nervous mechanism of the 

 vertebrate to the administrative organization of any efficiently 

 managed commercial enterprise. There are the different phases 



