228 OF SENSATION, AND THE ORGANS OF THE SENSES. 



tones. It is well known that instances exist in which, from some imperfec- 

 tion in organization, there is an incapacity for distinguishing colours or musical 

 tones, whilst there is no want of sensibility to light or sound ; and that some 

 persons are naturally endowed with a much greater range of the sensory 

 faculties than others possess. Hence it does not seem at all improbable, that 

 there are properties of matter of which none of our senses can take immediate 

 cognizance ; and which other beings might be formed to perceive, in the same 

 manner as we are sensible to light, sound, &c. Thus, it is well known that 

 many animals are affected by atmospheric changes, in 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 same influences. Now the 

 most universal of all the qualities or properties of matter, that, in fact, on 

 which our notion of it is founded, is resistance; and it is this quality, of 

 which the knowledge seems most universally diffused throughout the Animal 

 kingdom. In the lowest tribes, we find that contact between their surface 

 and some material body is required to produce sensation ; and beings which 

 cannot be made conscious, in this manner, of the existence of something ex- 

 ternal to themselves, do not deserve to be ranked in the Animal kingdom. 

 Our difficulty lies (as heretofore remarked, 113), in ascertaining what are 

 to be regarded, in such beings, as unequivocal indications of consciousness. 

 Those animals which are fixed to one spot, can have few other ideas of matter 

 than this most general one ; but in those which have the power of locomotion, 

 the general sensibility of the surface doubtless communicates to them some 

 notion of the character of the body over which they move, in the same manner 

 as we learn it by passing the hand over its exterior. 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 ; which animals of the lowest grade can 

 scarcely be supposed to exercise. There can be no doubt that, next to the 

 mere sense of resistance, sensibility to temperature is the most universally 

 diffused through the Animal kingdom; and probably the consciousness of 

 luminosity is the next in the extent of its diffusion. There is good reason to 

 believe, from observation of their habits, that many animals are susceptible of 

 the influence, and are directed by the guidance of light ; whilst their 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 

 prominent parts of Animalcules, the lower Articulata and Mollusca, and even 

 of some Radiata. Wherever these are of sufficient size to allow their struc- 

 ture 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. 

 The sense of Taste may be considered as a refined modification of that of 

 touch ; and it is probable that this 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 so 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 ; and this would appear, from a 

 fact subsequently to be mentioned ( 320), to be not improbably the case with 

 regard especially to aquatic animals. 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. 



