178 SMELL, TASTE, ALLIED SENSES 



ations from the reception of the stimulus to those central 

 changes that mark the entrance of the impulse into the 

 central organ including the production of a sensation, 

 if such occurs. 



Where a recept is concerned with sensation, the pro- 

 duction of this state may be regarded as its final step. A 

 sensation, then, is an activity in a particular region or 

 spot of the central nervous organ marking the central 

 end of the receptive portion in a reflex arc. Experience 

 has shown that, irrespective of the means by which this 

 central region is stimulated, it calls forth only one kind 

 of sensation. This in a way is a restatement of the mod- 

 ern view of Miiller's specific energy of the nerves, for, 

 according to this principle, however a particular sense 

 organ, or conducting trunk, or nerve center may be stim- 

 ulated, only one kind of sensation results. In other 

 words the character of a sensation is not determined by 

 peripheral organs but is strictly a central affair and sen- 

 sations are different not because of the different sources 

 of the incoming impulses, but because of the different 

 central spots excited. Since the anatomical connections 

 are such that a particular receptor always leads to a 

 special central region, it follows that such a receptor be- 

 comes thus associated with a given sensation. Hence 

 where sensations occur they may be used in distinguish- 

 ing receptors, but in the many recepts that are unassoci- 

 ated with sensation this feature naturally cannot be called 

 upon as a means of discrimination. 



Although numerous receptors are in no way concerned 

 with sensations, there are no receptors that are not ac- 

 tuated by stimuli. Hence the stimulus affords a more 

 general basis for discriminating between receptors than 



