considered in connexion with General Sensation. 187 



the surface of water (putting aside the effect of sensible heat) 

 only conveys information of the presence of the liquid by the re- 

 sistance called into action by pressure. Then the molecules of the 

 liquid seem to impinge on the sense of touch after the same man- 

 ner as solids. And so, too, air in motion makes itself felt 

 (putting aside the difference of temperature) by the resistance 

 it opposes to the proper sense of touch. In addition to the above 

 considerations, we may observe that it is by the sense of touch the 

 mind is made acquainted with the size, form, and other external 

 features of bodies, remarking that such attributes belong only 

 to the solid condition of matter. Again, the sense of taste has 

 especial reference to the liquid state of matter, its proper nerves 

 being affected only by matter in that condition. Physiologists 

 make the fundamental condition for the perception of taste to be 

 the solution of the sapid substances in the secretions of the organs 

 of taste. Substances to be tasted must either be in solution, or be 

 soluble in the moisture covering the tongue ; insoluble substances 

 produce merely sensations of touch. Hence w r e should expect be- 

 forehand that the surface in which the sentient nerves of taste 

 terminate should be moist in order that the action may be uni- 

 formly carried on. And this is the case. When the tongue and 

 fauces are dry, sapid substances even in solution are with diffi- 

 culty tasted. Finally, the sense of smell has reference to the 

 gaseous condition of matter. It is only when a solid becomes 

 volatilized that the olfactory nerves can be affected by it, and 

 liquids can only reach this avenue of sensation in the shape of 

 vapour. The nerves can only be impressed by substances in a 

 state of extremely line division in the atmosphere or gaseous ex- 

 halations. In the act of smelling the odorous matter is trans- 

 mitted in a current through the nostrils. Thus this sense is 

 brought into play by the ordinary respiratory movements, and the 

 impression can be intensified by what is called sniffing. The man- 

 ner, then, in which matter is conveyed to the nerves of smell is 

 consistent with the view that this sense is specially intended for 

 the gaseous condition of matter. 



Secondly, in the case of all these three senses alike actual con- 

 tact with the nerve by the substance under examination is neces- 

 sary ; we may, in fact, regard them as subsenses, and include 

 them under the common heading of Tact. The prehensile shape 

 itself of the proper organ of touch suggests that contact must 

 take place before that sense can bo called into play. We all 

 know also that we cannot taste a thing except we put it into the 

 mouth and a contact be effected with the gustatory nerves. Nor 

 can the nerves of smell receive an impression from a remote sub- 

 stance through another, the matter to be examined must itself 

 enter the organ : the olfactory nerves must actually be touched 



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