g APPENDIX. 



siderthe subject. The relations, however, which evidently subsist between that form 

 of sensibility, called organic sensibility by Bichat, and the animal instincts, are much 

 more numerous, distinct, and intimate. 



Organic Sensibility refers to those sensations which are produced in different degrees 

 of intensity, owing to the existence of certain conditions of those viscera which are im- 

 mediately subservient to the preservation of the individual and the species to nutrition 

 and reproduction, and which are not immediately subjected to the influence of volition. 

 The conditions of the parts exciting- sensibility are very various, and are the result of 

 irritations arising from the presence of a stimulus, of unnatural actions supervening in 

 particular systems or textures, and of the deficiency of that stimulus or influence to 

 which particular viscera have become accustomed. Many of the changes preceding 

 this class of sensations, seem to interest, in the first instance, the ganglial class of nerves ; 

 but, owing to the intimate relation existing between this part of the nervous system and 

 the voluntary or sentient part, the impression or change is propagated to the brain. 

 This is the only essential difference which subsists between this and the other forms of 

 sensibility. It is the brain which perceives in them all ; and, although stimuli, or the 

 defect of stimuli, may give rise to certain phenomena possessing the characters of the 

 higher manifestations of this property, in the organs appropriated to the preservation of 

 the organic system, independently of the sensorium, consciousness or the more perfect 

 form of sensibility, cannot form part of the results. 



Organic sensibility may be active or passive it may, or it may not, be attended with 

 consciousness ; and even the inconscious mode of it may indirectly impel to action, or 

 give rise to many of the manifestations or instincts which characterize the lower ani- 

 mals, owing to the ganglial centres, either from their organization or connexions, or 

 from both, performing a greater extent of functions than generally falls to their share. 

 I^ therefore, the passive form of organic sensibility may propel to action without con- 

 sciousness or the sensorial sensibility being excited in these animals, we may also ac 

 count in the same manner, for many of the instinctive functions being performed when 

 we cannot trace them to the influence of a cerebral organ. Of all the conditions of 

 sensibility, its active organic form is the least under the controul of the mental energies 

 of the individual in which this form of sensibility is developed. It also, in all its modes 

 of existence, more intimately interests the existence of the individual than the other 

 forms of sensibility, it involves a feeling instinctive of life or death in all its active ma- 

 nifestations. 



From this it will be readily seen, how close a connexion exists between organic sen- 

 sibility and the animal instincts : it does not belong to our plan to trace the connexion 

 In all its relations. 



Of sensibility, generally, we may observe that, in the human species, it is very varia- 

 ble ; in some persons it is very much exalted, in others very obtuse. It is vivid in early 

 life and in youth ; after the age of manhood, it gradually diminishes ; as old age advan- 

 ces, it decreases rapidly; and, in persons who have attained a great age, it is present in 

 the lowest grade, in which we find it in the species. 



Contractility is essentially a vital phenomenon, and it is the result of a change in the 

 relative position of the molecules composing the solids of a living body. This property 

 may be divided into the following grades, commencing with the lowest, it being the 

 most generally diffused throughout nature : 



1. Insensible Organic Contractility, or, that usually denominated tone or tonicity. This 

 grade of contractility is not confined to the animal kingdom ; it is a property of vegeta- 

 bles, and of animals not possessed of a heart. It is diffused throughout the tissues. The 

 vascular system possesses it in the most eminent degree ; and it may be viewed as the 

 result of the vital influence with which the structures are endowed ; it is more or less 

 perfect as the vital energy is perfect, and it disappears with the extinction of this prin- 

 ciple. It is a property of the tissues and of the vessels, which is more or less exerted in 

 all the vital operations ; in the circulation, the secretions, nutrition, and absorption. 

 The ganglial or organic class of nerves seem to be instrumental in its production and 

 preservation, in the animal kingdom. 



2. Sensible organic contractility^ or irritability, is that inherent property of contraction 

 which exists in a!l muscular, and in some other textures. It is excited by the applica- 

 tion of a variety of irritants. It seems to depend upon the ultimate distribution of the 

 nervous substance to these parts, and chiefly upon the nerves proceeding from the 

 ganglia. 



Both these species of organic contractility seem to result from one species of influ- 

 ence with which animal bodies are endowed ; they are the proximate result of vitality, 

 and merely differ from each other owing to the intimate structure of the parts in which 



