CHAPTER XXV 

 SENSE OF TOUCH OLFACTION GUSTATION 



Muscular sense Sense of touch Appreciation of temperature Olfaction Olfactory 

 (first nerve) Properties and uses of the olfactory nerves Mechanism of olfaction 

 Relations of olfaction to the sense of taste Gustation Nerves of taste Chorda 

 tympani Glosso-pharyngeal (ninth nerve) General properties of the glosso-pharyngeal 

 Relations of the glosso-pharyngeal to gustation Mechanism of gustation Physio- 

 logical anatomy of the organs of taste Taste-beakers. 



THE senses of smell, taste, sight and hearing involve peculiar 

 organs, provided with nerves having special properties that usually are 

 not endowed with what is described as general sensibility. These 

 nerves have been omitted in the general description of the nervous 

 system, as well as the organs in which they are distributed. 



Sensations of pain, touch, contact (localization), temperature, weight, 

 pressure and the so-called muscular sense, are all conveyed to the senso- 

 rium by what have been described as centripetal nerves, the sense of 

 touch being perfected in certain parts by peculiar structures at the end- 

 ings of the nerves. The muscular sense, by which weight and resistance 

 are appreciated, undoubtedly depends largely on the muscular nerves. 

 The above subdivisions are sufficiently distinct so far as the character 

 of the sensations are concerned ; and it remains to see whether they 

 pass to distinct centres by special paths of conduction or are conveyed 

 by what are known as nerves of general sensibility. As regards this 

 question, physiologists have to rely mainly on experiments on the human 

 subject, and pathological observations. 



The general sensory nerves are sufficiently distinct in their proper- 

 ties from the true nerves of special sense. The latter convey peculiar 

 impressions only, such as those of sight, hearing, smell and taste. The 

 former, when strongly stimulated or irritated, always convey impressions 

 of pain. Separating, then, all other senses, except the venereal sense, 

 from the true special senses, it is proper to inquire whether it be reason- 

 able to assume that any of the varieties of general sensation require 

 special nerves for their conduction. 



It is well known that a relatively strong stimulation of a sensory 

 nerve or of sensitive parts is necessary for the production of a painful 

 impression ; and it is also well known that very painful impressions 

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