172 Rev. P. Keith o?i the Susceptibilities of Living Structures. 



Man, who stands at the head of the animal creation, exhibits 

 the strongest indications of sensibihty, the largest propor- 

 tion of brain, and the most complicated structure of organs, 

 rendering him capable not only of sensation and of perception, 

 but also of volition and of intellection. — This is the animal 

 sensibility of Bichat, having the brain for its principal organ*. 

 It is direct, or it is sympathetic. The gratification of tlie 

 sexual appetite gives direct pleasure; — the sensation of hun- 

 ger or of thirst gives direct pain. Labour induces the direct 

 feeling of fatigue ; — sleep and rest induce the direct feeling of 

 recruited or renovated strength. If the nerve leading to the 

 one eye happens to be affected, the nerve leading to the other 

 eye is apt to become sympathetically affected also. If we see a 

 fellow-creature in distress, or if we see even a brute animal 

 exposed to torture, or convulsed in the agonies of death, we 

 cannot divest ourselves of a feeling of sympathy. 



Such are the two sensibilities corresponding to the two 

 lives of Bichat. Organic sensibility is the faculty of receiving 

 an impression ; — animal sensibilit}'^ is the faculty of receiving 

 an impression, and of transmitting it to a common centre of 

 feeling. Organic sensibility lingers for a time in the several 

 organs, even when life is gone; — animal sensibility is extin- 

 guished with life, be the extinction ever so sudden. Organic 

 sensibility commences with the foetus; — animal sensibihty not 

 till after the birth. The former regards the preservation of 

 the individual, and cannot intermit; — the latter regards its 

 communication with the external world, and has frequent 

 intermissions. Organic functions are perfect at once, and are 

 not performed better in the mature individual than in the 

 infant animal or plant; — animal functions are perfected by 

 experience and education. The eye does not at first distin- 

 guish specific objects, nor the ear specific sounds, nor the 

 palate specific tastes; but the habit of using the several organs 

 of sense gives at last the power of due discrimination, and the 

 tact necessary to quick perception. 



From the above contrast it is evident that animal sensi- 

 bility is of a grade superior to organic sensibility: and yet 

 there are cases, as we have already seen, in which the latter 

 may be exalted into the former by the application of certain 

 means, or the intervention of certain causes. A certain dose 

 of sensibility gives organic feeling, — a certain other dose gives 

 animal feeling. — The blood traverses the veins, heart, and 

 arteries without being felt. In its pure and uncontaminated 

 state it merely excites the organs to healthy action. But 

 augment its sensibility by the admixture of certain foreign in- 



• Rechcrchtt Phya. p. 63. 



gredients, 



