OP SENSIBILITY IN GENERAL. 723 



such a manner that their actions are regarded by Man as indications of the 

 probable state of the weather; and the same is the case in a less degree with 

 some of our own species, who are peculiarly susceptible of the like influences. 

 Now the most universal of all the qualities or properties of Matter, on 

 which, in fact, our notion of it is chiefly founded, is its occupation of space, 

 producing a more or less complete resistance to displacement ; and this quality 

 is that through which alone any knowledge of the external world can be ob- 

 tained by a large proportion of the lower Animals ; contact between their 

 own surface and some material body, being required to produce sensation. 

 We shall presently see, however, that the idea of the shape of a body which 

 we form from the touch, results from a very complex process, such as ani- 

 mals of the lower grades can scarcely be supposed to exercise. There can 

 be little doubt that, next to the mere sense of resistance sensibility to tempe- 

 rature is the most universally diffused through the Animal kingdom ; and 

 probably the consciousness of luminosity is the next in the extent of its diffu- 

 sion. 1 It is probable that the sense of taste (which has a close affinity to 

 that of touch) exists very low down in the animal scale, being obviously of 

 great importance in the selection of food ; but the Anatomist has no means 

 of ascertaining where this refinement exists, and where it does not; since the 

 organs of taste and touch are very similar. The sense of hearing does not 

 seem to be distinctly present among the Invertebrate animals, except in 

 such as approach most nearly to the Vertebrata ; it is not improbable, how- 

 ever, that sonorous vibrations may produce an effect upon the system of 

 those animals which do not receive them as sound. The sense of smell, 

 which is concerned with one of the least general properties of matter, appears 

 to be the least widely diffused among the whole ; being only possessed in 

 any high degree by Vertebrated animals, and being but feebly present in a 

 large proportion of these. 



591. Besides the various kinds of sensibility which have been just enumer- 

 ated, there are others which are ordinarily associated together, along with 

 the sense of material resistance (and its several modifications), and the sense 

 of temperature, under the head of Common Sensation ; but several of them, 

 especially those which originate in the body itself, can scarcely be regarded 

 in this light. Such are the feelings of hunger and thirst; that of nausea ; 

 that of distress resulting from suspended aeration of the blood ; that of 

 " sinking at the stomach," as it is vulgarly but expressively described, which 

 results from strong mental emotion ; the sexual sense, and perhaps some 

 others. Now in regard to all these, it is impossible in the present state of 

 our knowledge to say, whether their peculiarity results from the particular 

 constitution of the nerves that receive and convey them, or only from a 

 modification of the impressing causes, from the particular endowments of 

 their gangliouic centres, and from the mode in which they operate. Thus 

 we have no evidence whether the nervous fibrils which convey from the 

 lungs the sense of distress resulting from deficient aeration, are of the same 

 or of a different character from those which convey from the surface of the 

 air-passages the sense of the contact of a foreign body. But as we know 

 that all the trunks along which these peculiar impressions travel, do min- 



1 There is good reason to believe, from observation of their habits, that many ani- 

 mals are susceptible of the influence, and are directed by the guidance of light, whose 

 organs are not adapted to receive true visual impressions, or to form optical images ; 

 and such would seem to be the function of the red spots, frequently seen on promi- 

 nent parts of the lower Articulata and Mollusca, and even of some Radiata. Wherever 

 these are of sufficient size to allow their structure to be examined, they are found to 

 be largely supplied with nerves, but to be destitute of the peculiar organization which 

 alone constitutes a true eye. 



