m their Stnicture mid Futictions, 123 



it into hearing, and the gustatory and olfactory nerves into 

 taste and smell. The sense of touch, besides being distri- 

 buted over the whole surface of the body, possesses, in the 

 mammal class of animals, and in some birds and insects, its 

 peculiar local organ, as well as the other senses. In man, the 

 local organ of touch resides in the tongue, the lips, and the 

 points of the fingers : in the horse it exists in the nose and 

 tongue, and in the pig it is situated in the snout. We find, 

 however, that those animals which possess a local organ of 

 touch of a complete and perfect kind, and capable of receiv- 

 ing the most delicate impressions, are all furnished with a 

 brain and a complicated nervous system ; but in the inferior 

 tribes of animal beings, as the mollusca, shell-fishes, and the 

 larvae of insects, in which the sense of touch has no local 

 organ, but is merely diffused over the general surface of the 

 body, the brain is entirely wanting, and the nervous system 

 is of a less perfect conformation. From the most satisfactory 

 evidence, then, it seems that the faculty of general touch or 

 feeling, or common sensation as it is called, is the most simple 

 and common of all the senses ; and that the presence of a 

 brain is not necessary to its existence, for it is as strikingly 

 displayed in the lowest orders of animals as it is in those 

 which are the most highly organised. Now, it has been ob- 

 served that temperature produces upon plants effects which 

 cannot be referred to any of its mechanical or chemical ope- 

 rations ; we can therefore scarcely entertain a doubt that they 

 are furnished with organs adapted to receive the impressions 

 of heat and cold ; in other words, that they possess the nerves 

 of the sense of touch. Whether plants are susceptible of 

 the pressure of contiguous bodies is less certain ; but even if 

 they be not so, still the possibility of their possessing nerves 

 of touch is not destroyed or diminished ; for it seems that 

 these nerves are divided into two distinct sets, because it is 

 found that we possess a sensibility to temperature, and also 

 a sensibility to resistance, and these two bear no proportion 

 to each other. Cases are not wanting in which individuals 

 have been sensible to the impressions of temperature, and yet 

 have been insensible to those of resistance ; others, again, have 

 occurred where sensibility to resistance has remained perfect 

 and sound, while that to temperature has been completely 

 lost. Since, then, the sensations of heat and cold reside in 

 nerves distinct from those which form the seat of the sens- 

 ations of resistance, it is clear that a living body may possess 

 the former, and yet be destitute of the latter ; so that, although 

 plants may be incapable of feeling the resistance of bodies 

 placed in contact with them, they may nevertheless be sensible 



