INTERNAL SENSATIONS. 299 



it an hermaphroditic sensation, inasmuch as, whilst it excites laughter, 

 it is insupportable; and, consequently, seems to be intermediate between 

 pleasure and pain. 



c. Internal Sensations. 



The external sensations make us acquainted with the universe sur- 

 rounding us ; and convey to the mind a knowledge of every thing that 

 can be, in any manner, inservient to our necessities. Such necessities 

 have, however, to be suggested to the mind, before it reacts through 

 the aid of the organs of prehension or otherwise on external bodies, 

 and this is accomplished by the internal or organic sensations. 



Without the intervention of an external cause, every organ of the 

 body is capable of transmitting to the encephalon a number of different 

 impressions, many of which impel the organs to acts that are necessary 

 not only for the preservation of the individual and of the species, but 

 also for the perfect developement of the faculties. Such are the sensa- 

 tions of hunger and thirst ; the impulse that leads to the union of the 

 sexes ; and the feeling we have of the necessity for intermission in the 

 exercise of the muscles, and the intellect. They have been divided 

 into three species by some physiologists ; the first arousing, or giving 

 impulse to, the action of organs, and warning the brain of the different 

 necessities of the system. They have been called wants or instinctive 

 desires. 1 Such are hunger, thirst, the desire to evacuate the urine and 

 faeces; that of respiration, the venereal appetite (le genesique, amour 

 physique), accouchement, &c. They belong to those that arise, when 

 it is necessary the organs should act. The second occur during the 

 action of organs. They are often obscure, but sometimes acute. 

 Amongst these are the impressions accompanying the different excre- 

 tions, as of the sperm, urine, &c. (although, as we have seen, these 

 partly belong to the external sensations); the impressions that warn 

 us of our partial or general movements, of the progress of digestion, 

 and of intellectual labours. The last succeed to the action of organs, 

 especially when such action has been too long continued ; hence the 

 inward feeling of fatigue after too long exertion of the functions of 

 the senses, of the intellectual and moral faculties, and of the organs of 

 muscular motion ; the necessity of repose after prolonged muscular 

 exertion ; and of sleep, to recruit the nervous system, and to fit it for 

 the exertions it has to make during the waking condition. 



.The mode in which these sensations are effected is analogous to that 

 of the external sensations. There is an impression on the part to 

 which the sensation is referred; an action of perception accomplished 

 by the encephalon ; and one of transmission, executed by a nerve 

 passing between the two. The last two actions are probably execute'd 

 in the same manner as in the external sensations. The first, or the 

 mode in which the impression is effected, and the character of the im- 

 pression itself, are more obscure. In the external sensations, we can 

 refer the impression to a known irritant, special in some of the senses: 



1 Adelon, art. Besoins, in Diet, de Medecine, i. 367, Paris, 1821; and Physiologic de 

 1'Hornme, i. 482. 



