PHYSIOLOGY OF OLFACTION 87 



protective odor in that it implies that it can be sensed 

 by other animals that will thereupon avoid its source. 

 The great delicacy of olf action among the higher animals 

 by which they can scent the hunter is well known. Other 

 odors have much to do with sexual activities whereby one 

 sex is led to find the other or is otherwise excited to ac- 

 tivity. But the prime service of olfaction is in the quest 

 of food. From the fishes to the mammals olfaction 

 serves as a means of discovering hidden or remote food 

 and in this respect it is a highly significant sense for the 

 direction of locomotion. In man and other microsmatic 

 forms much of the keenness of olfaction has disappeared 

 and yet the high development of this sense in our an- 

 cestry has left such a profound impression on the 

 organization of our central nervous apparatus that we are 

 often surprised by the power of our olfactory associations. 



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