CHAP. XXXV.] THE SENSES. 93 



touch. Perhaps, however, this is little else than a merely 

 verbal question. 



There are several different ways in which the various 

 senses differ very remarkably from one another. These 

 differences I shall now proceed to enumerate. 



1. The nerves of the skin are both nerves of touch and The 

 nerves of the sense of heat ; and the nerves of the inside ^'^j.^gg .^^.^ 

 of the mouth are nerves at once of touch, of the sense of ueives of 

 heat, and of taste. These, though combined in the same and heat ; 

 nerves, are distinct senses ; and when the same nerve is ^® ^^'^ ^^^° 



. . . „ , . . , the nerves 



transmitting sensations or distinct senses to the sensory of taste ; 

 ganglia, they are cognised by the consciousness as distinct 

 sensations. Thus, if we are eating something which is and these 

 hard enough to press against the inside of the mouth, ''^^'^■''atioiis 

 which is hot, and has a flavour, the pressure, the heat, and combine 

 the flavour form, not one combined sensation, but three other T^ ' 

 distinct sensations. But when two or more sensations of 

 the same sense are transmitted by the same nerve, the 

 sensations, instead of being cognised as distinct, combine 

 into a resultant sensation, which makes a single impres- 

 sion on the consciousness. Thus, if two tastes, or two hut two 

 smells, are mixed together, the mixture is perceived as a smeifs°'^ 

 single taste or smell, having a character intermediate 'wlien 

 between those of its constituents ; but it is impossible to combine 

 direct the attention to one of the two constituents sepa- "1*° f 



. . . ^ resultant 



rately. In drinking tea with sugar in it, for instance, the of charac- 

 sensation is a mixed sensation, and not two sensations ; ^^ediate^' 

 and it would be impossible, by any effort of attention, to i^etween 

 taste the tea and not the sugar, or to taste the sugar and stituents.' 

 not the tea. The same is true of mixed colours. If two So of 

 rays of light of different colour are made to combine their ^^^^^ 

 colours by falling on the same spot of white paper, what 

 is seen is not two colours, but a resultant colour. If red 

 and yellow, for instance, are thus combined, the resultant 

 colour is orange ; and it would be impossible, by any effort Orange, 

 of attention, to see either the red or the yellow separately. 

 In some cases, of which that just mentioned is one, the 

 resultant colour is of a character intermediate between 

 those of its constituents ; but when all the prismatic 



