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CHAPTEK III. 



THE SENSE OF SMELL. 



The organ of smell is, in vertebrate animals, embedded in 

 the mucous membrane of the nostrils, and in mammalia 

 can generally be distinguished by its yellow or brownish 

 colour. In birds, on the contrary, it presents hardly 

 any peculiarity to the naked eye. For our knowledge 

 of the minuter structure we are mainly indebted to 

 Max Schultze. The cylindrical epithelial cells in the 

 olfactory organs of man (Fig. 31) terminate in broad flat 

 ends. Between them are rod-like filaments, which are 

 supposed to expand into a ganglionic cell, terminating 

 in a nerve-fibre. Schultze terms these olfactory cells. 



In other cases, as in birds, Amphibia (Fig. 32), etc., 

 the olfactory cells terminate in fine ciliaa, or olfactory 

 hairs, either one or many to each cell. These hairs 

 are sometimes motionless, sometimes have a slight 

 movement of their own. It is obvious that no one from 

 the structure alone could have predicated the function ; 

 nor can we, I think, form to ourselves any satisfactory 

 conception how such a structure conveys the impression 

 of smell, or in what consist the difi'erences between 

 different odours. 



If, then, we know really so little as to the mode, or 

 organs, by which the sense of smell is induced among 



