OF SENSIBILITY, 7 



r.ll classes of animals are endowed, and which, in the lowest orders and in some vege* 

 tables, assumes the appearance of sensibility. In these, however, we have no reason 

 to infer the presence of sensibility, merely because they contract under the influence 

 rfa stimulus; for the contraction may take place without the existence of this property, 

 from the effect produced by the stimulus upon the organization of the contracting- part. 

 Indeed we cannot suppose that sensibility is present where the parts generally observed 

 to be instrumental in its production are not found to exist ; a sensation cannot be sup- 

 posed to be produced where there neither is an organization suitable to receive, a. 

 channel to convey, or p.n organ to perceive an impression. We should, therefore, limit 

 this term to those phenomena, which the author arranges under that of perceptibility. 



With this limitation, sensibility may be called the function of sensation, and a property 

 peculiar to the animal kingdom. The sensations are derived through the medium of 

 the senses, and of the nerves, which are distributed to certain parts of the body, and 

 which communicate with the encephalic centre. On this centi-e the existence of sensi- 

 bility chiefly depends : the ramifications of its nerves, or the subordinate portions of- it, 

 being also parts of the apparatus requisite, but not giving rise to this property. As we 

 ascend in the scale of creation, and as we perceive the senses, and the organs of voli- 

 tion in more intimate relation with this nervous mass the encephalon so we find sen- 

 sibility becoming more perfect, until, in man, it reaches an extent greatly surpassing 

 that in which we observe it in any other animal. 



In man, and perhaps, in the more perfect animals, the modes of sensibility seem to 

 vary. These modes may, however, be divided into two conditions, as they are more oi f 

 less active ; namely, conscious or active sensibility, and inconscious or passive sensi- 

 bility : the former relates to these impressions, either from within or from without, 

 which give rise to perceptions or ideas, the latter to those that are frequently produced 

 upon the senses and upon the ramifications of the cerebral nerves, and, owing either to 

 habit or the want of due attention to them, are not perceived by the mind. In this lat- 

 ter mode of sensibility, the organ receiving, and the channel conveying, the impression, 

 perform their offices, but the mind either is not, at the time when the impression is 

 made, in a state to receive it, or receives it so imperfectly, from its weakness or its 

 transient nature, as not to give rise to consciousness. This mode does not necessarily 

 imply a difference in the degree of sensibility, but a condition in which it exists, owing 

 either to its being excited by other impressions, or to its enjoying repose from being 

 exhausted at the time when the impression is made ; it is a state to which the highest 

 manifestations of sensibility, as well as the lowest, may be occasionally subject. It is, 

 however, merely a relative mode of this property, and the relation subsists entirely be- 

 tween the state of the cerebral organ which perceives, and the force and duration of the 

 impression made upon the organ of sense. Thus when the sensibility is actively occu- 

 pied with a particular object, and an impression is made at the same time upon a dif- 

 ferent organ from that through which the perception, with which the mind is engaged, 

 was conveyed ; the second impression may affect the senses in an evident manner, and 

 even so as to influence volition, yet we may be inconscious of its operation, and no ac- 

 tive perception may result from it. If, however, the second impression be stronger or 

 more vivid than the first, or if, from various circumstances besides, it should excite the 

 cerebral functions, active sensibility or consciousness is the result. 



As sensibility, according to this view of the subject, is, in its active state, aterm mere- 

 ly expressive of consciousness in the entire range of this very generally diffused faculty 

 of the nervous system ; and as this faculty is evidently dependent upon this system, es- 

 pecially on the more complex part of it which holds relation with surrounding objects ; 

 and also as we have no reason to attribute the possession of this part of the nervous sys- 

 tem, to the very lowest orders of animals, particularly to the class Radials, so we must 

 conclude, that, although a property of animal life, its higher grades are not possessed 

 by all animals. It may be also stated, that active sensibility, being considered as ex- 

 pressive of the consciousness of the whole class of sensations, and all the intellectual 

 and moral operations, varies in its extent throughout the animal kingdom, according as 

 those manifestations are more or less numerous and perfect. How far the passive mode 

 of sensibility, or that unattended by consciousness, may be the property of a lowest 

 orders of animals, is difficult to say. We may, however infer, that, as this condition of 

 sensibility may take place without an active exertion of this property in the highest 

 animals, so it may result from a less perfect endowment of sensibility in the lower; ami 

 as this mode may require a less complex apparatus for its production, inasmuch as its 

 relations are more simple, so It may be possessed by animals, whose organization and 

 manifestations do not permit us to conclude that they are capable of evincing sensibility 

 in its more perfect and active conditions. The relations which this form or mode of 

 sensibility hold with the numerous instincts of animals, must be evident to all who con- 



