NEURO-MUSCULAR MECHANISM 



DISTANCE RECEPTORS 



(a) FOE CHEMICAL STIMULI 

 Sense of Smell 



Smell, as Sherrington puts it, is taste at a distance. Just 

 as the taste organs are stimulated by substances taken into 

 the mouth, so the olfactory organs are stimulated by volatile 

 substances inhaled through the nose. 



The olfactory organs are the most fundamental of all 



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FIG. 51. The Connections of the Olfactory Fibres. A, olfactory cells ; B, 

 synapses in the olfactory bulb I. ; ii., olfactory tracts; iii., olfactory 

 centre ; iv., decussation of fibres. (HowELL.) 



distance receptors, and they play a most important part in 

 the life of the lower animals in guiding them to their food and 

 repelling them from danger, in causing positive and negative 

 chemiotaxis. In such animals the mechanism is very highly 

 developed. 



1. Receptors. Over the upper part of the nasal cavity the 

 columnar epithelial cells are devoid of cilia, and between them 

 are placed spindle-shaped cells (fig. 51, A), which send processes 



