CHAP. VIL] OF THE SENSES OF TASTE AND OF SMELL. 



413 



with a thin bacillum (or bacillarium), with a transparent and 

 crystalline extremity (Fig. 74). At their inferior part, these 

 cells emit nodose filaments, which 

 continue with the fine ramifica- 

 tions of the olfactory nerves. 1 



The sense of olf action, even in 

 man, is of very great delicacy. An 

 air charged with a ten-thousandth 

 of its volume of vapour of essence 

 of roses has nevertheless for us an 

 extremely appreciable odour. The 

 keenness of the sense of smell is 

 far greater still in many animals, 

 capable of catching numerous 

 scents which escape us. 



In reality, spite of the vola- 

 tility of scented substances, the 

 manner in which these substances 

 enter into relation with the ol- 

 factory elements does not differ 

 essentially from what takes place 

 for the sense of taste. The ol- 

 factory mucous membrane being 

 constantly lubricated by a secre- 

 tion, it is always in the state of 

 solution that the scented particles 

 come into contact with it. Also 

 the groups of olfactory and gus- 

 tatory sensations are very near 

 neighbours, and it is not without 

 difliculty that physiologists are 

 able to distinguish them. In sum, 

 smell is akin to taste, and taste is akin to touch. Strictly, we 



PIG. 74. 



Microscopical elements of the olfactory 

 mucous membrane : 1, of the frog ; a, 

 cylindrical nucleated epithelial cell, 

 terminating at its base with a ramified 

 filament ; &, nucleated cell of the olfac- 

 tory bacillum, c, which terminates at its 

 extremity with a bundle of long vibra- 

 tile cilia, e, while the cell bears at its 

 base a fine nodose filament, which con- 

 tinues with the fibres of the olfactory 

 nerve. 2, of man : a, the epithelial 

 caudal cells, between which are the 

 cells, 6, with their olfactory bacilla, c, 

 their terminations gemmate, e, and their 

 internal filaments, d, communicating 

 with the fibres of the olfactory nerve. 

 3, fibres of the olfactory nerve of the 

 dog, dividing themselves into very fine 

 fibrils. 



1 C. Vogt, Lcttr&s Physiologiques, p. 419. 



