276 SENSATION AND THE SENSIFEEOUS ORGANS. 



On the hypothesis which appears to me to be the 

 most convenient, sensation is a product of the sensifer- 

 ous apparatus caused by certain modes of motion which 

 are set up in it by impulses from without. The sensif- 

 erous apparatuses are, as it were, factories, all of which 

 at the one end receive raw materials of a similar kind 

 namely, modes of motion while, at the other, each 

 turns out a special product, the feeling which constitutes 

 the kind of sensation characteristic of it. 



Or, to make use of a closer comparison, each sensif- 

 erous apparatus is comparable to a musical-box wound 

 up ; with as many tunes as there are separate sensations. 

 The object of a simple sensation is the agent which 

 presses down the stop of one of these tunes, and the 

 more feeble the agent, the more delicate must be the 

 mobility of the stop.* 



But, if this be true, if the recipient part of the sen- 

 siferous apparatus is, in all cases, merely a mechanism, 

 affected by coarser or finer kinds of material motion, 

 we might expect to find that all sense organs are funda- 

 mentally alike, and result from the modification of the 

 same morphological elements. And this is exactly what 

 does result from all recent histological and embryologi- 

 cal investigations. 



It has been seen that the receptive part of the olfac- 

 tory apparatus is a slightly modified epithelium, which 

 lines an olfactory chamber deeply seated between the 



* " Chaque fibre est unc especc dc touche ou de martcau destin6 a 

 rendre un certain toil." Bonnet, " Essai de Psychologic," chap. iv. 



