112 PHYSIOLOGY OF FARM ANIMALS [CH. IX 



man, we find that tastes may be classified under four chief heads : 

 sweet, bitter, sour or acid, and salt. In order to taste a substance 

 it must first be dissolved, in order to act upon the gustatory cells. 

 The Sense of Smell. The sense of smell is very well developed 

 in animals and plan's a large jDart in their normal life and habits. 

 The organ of smell consists of a well-defined area of mucous 

 membrane lining part of the nasal cavities, and characterised by 

 the absence of cilia. This olfactory region, as it is called, is well 

 supj^lied with branches of the olfactory nerve, together with a few 

 fibres from the 5th cranial nerve. The olfactory mucous membrane 

 contains cells of two kinds, those associated with the production 

 of the sense of smell, numerous, long slender rod-shaped cells, and 

 others whose chief function is to suj^port the true olfactory cells 

 with which they are intermixed. The sensation of smell arises 

 through the stimulus of minute quantities of odoriferous matter 

 exciting the olfactory cells, the stimulus thus created being 

 carried back through the olfactory nerve to the brain. 



