THE NERVOUS SYSTEM OF MAN 1 65 



tex and structures immediately dependent upon 

 them, the old brain remaining on practically the 

 same level as in the kangaroo, except for the actual 

 reduction in man of some of the simple sensory 

 apparatus, notably the centers for the sense of 

 smell," (Figs. 50, 51.) 



Thus through these ancient routes of travel 

 passes all of man's sensory information. By the 

 right of long usage they have become fixed and 

 are not easily modified. Over these routes we 

 must believe travels all information about food, 

 enemies, dangers, recognition of offspring and 

 similar fundamental and universal stimuli. All 

 of the lower centers in the spinal cord and "old 

 brain" have remained in about the same condition, 

 while a few of the higher, associational, centers in 

 the dorsal portion of the anterior region of the 

 "old brain" have undergone profound changes re- 

 sulting in what is now termed the "new brain." 

 It seems to the writer that this must mean that the 

 regulation of alimentation, elementary forms of 

 adaptation involving protection and similar re- 

 actions are as old as life and that they became 

 fixed in form long before man existed. But man 

 has these common reactions with animals so we 

 must expect that when one of these ancient centers 

 becomes affected that recovery will be of necessity 

 much slower. It is generally conceded that "shell 

 shock" is a form of fear and it is easily conceiv- 



