314 A Manual of Veterinary Physiology. 



The odour of a body can be more certainly obtained by 

 ' sniffing.' This is an inspiratory act, producing a rarefac- 

 tion in the nasal chambers, which is overcome by more air 

 rushing in to restore equilibrium ; by this rushing in the 

 air is forcibly brought into contact with the olfactory area. 

 The sense of smell rapidly becomes blunted, the olfactories 

 apparently get used to an odour ; an unpleasant smell is 

 always more offensive when first detected than it is a few 

 minutes later. 



In connection with the nasal chambers are the facial 

 sinuses, which in horses and cattle are very extensive cavi- 

 ties filled with air, (which they derive from the nasal 

 chambers), and lined by a mucous membrane derived 

 from the Schneiderian. This membrane cannot distinguish 

 smell, according to Colin's experiments, nor should we 

 expect it to. 



The use of these sinuses is to make the head larger with- 

 out being heavier, and thus afford more surface attachment 

 for the muscles. During health the membrane lining the 

 cavities is moistened with a watery fluid ; but under 

 diseased processes, which are very frequent, the cavity 

 becomes filled with pus. 



By the sense of smell animals have the power of distin- 

 guishing good from bad, eatable from uneatable : and, 

 moreover, through this sense sexual activity is excited. 



Sensibility is supplied to the nasal chambers by the nasal 

 branch of the fifth nerve, not by the olfactory. 



Taste. 



The special nerve of taste is the glossopharyngeal, and 

 the portion of the mouth where the sense principally lies, 

 though not fully agreed on by physiologists, is the root of 

 the tongue and soft palate. The part of least taste, or no 

 taste at all, is the dorsum of the tongue ; this is due to the 

 dense coating of epithelium. 



The glosso-pharyngeal nerve consists of medullated and 

 non-medullatcd fibres ; the former terminate in end bulbs, 

 the latter in taste goblots (M'Kondriek). 



