ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 461 



sub-conscious reflexes referred to are still intact. Such a 

 dog, however, makes no difference between an obstacle, as 

 a dish of food, or a dangerous or threatening obstruction. 

 He is able to make no conscious interpretation, and by his 

 sub-conscious centers both the inviting food before him or 

 the threatening rod are mere obstacles to be avoided lest he 

 should run against them. 



Leaving now all of these lower centers of the nervous 

 system we reach finally the cerebrum itself, where, as far 

 as we know, the nerve centers have associated with them 

 for the first time that peculiar property which we are wont 

 to designate as consciousness. 



THE PHYSIOLOGY OF THE BRAIN AND THE LOCALIZATION 

 OF CENTERS. 



The careful work of such men as Jackson, Hitzig, 

 Fritsch, Beevor, Horseley and Ferrier has enabled us to 

 mark off the physiological topography of the cortex of the 

 brain and to establish for definite portions of the cortex 

 certain specific and definite functions. Their researches 

 have completely disproved the older notion that the entire 

 brain acted as a unit in every brain act; that a sensation, or 

 a volition, or a memory were actions participated in by the 

 entire brain as one structure. We now know that memory 

 is no such a simple thing, but that in certain portions of 

 the brain are stored auditory sensations, in other visual 

 sensations, and so on. We know that in certain portions of 

 the brain the voluntary impulses arise that move the foot ; 

 in other definite regions those that govern the movements of 

 the hand. It has even been possible by pathological ob- 

 servations to establish the position of the center of speech. 

 The topography of the brain as given in the accompanying 

 diagram is that now generally accepted. 



The position of these centers has been determined ex- 

 perimentally in one or more of the following ways : 



First. It not infrequently happens that persons are born 

 possessing certain brain malformations. By the post mortem 

 30 



