PHYSIOLOGY. 



of the brain has led some to suppose, that 

 particular powers resided in certain emi- 

 nences or depressions of the brain ; and 

 this is the foundation of the peculiar no- 

 tions of Dr. Gall, whose speculations have 

 attracted so much notice. He contends, 

 that the inequalities of the brain's surface 

 are the seat of the mental powers, and of 

 the various proensities, &c. of the human 

 species ; and that these are accompanied 

 by corresponding irregularities of the 

 skull, discernible by external inspection. 

 The whole fabric of his speculations is, 

 however, too visionary for serious refuta- 

 tion. See Rees's " Cyclopedia," article 

 CRANIOLOGY. 



The consideration of the various men- 

 tal powers belongs to the science of me- 

 taphysics, and will be pursued under the 

 proper articles. 



Sleeping and Watching. Sleep is the 

 repose of the organs of sense, and of the 

 voluntary motions, by means of which the 

 communication of the senses with exter- 

 nal objects is interrupted. It is the re- 

 sult of that law, which subjects the ac- 

 tions of the exterior or animal life to pe- 

 riods of intermittence. The most perfect 

 sleep is that in which all the functions of 

 this class are suspended, as the sensa- 

 tions, perception, imagination, memory, 

 judgment, locomotion, and the voice ; the 

 least perfect affects only a single organ. 

 Between these extremes, every gradation 

 may occur ; and, from the partial suspen- 

 sion of some functions, while others are 

 going on, arise dreams, and the various 

 phenomena of somnambulism. It is, 

 however, the same principle, whether 

 observed in the relaxation that follows 

 the contraction of a voluntary muscle, 

 or in the entire suspension of the animal 

 life. 



Watching may be considered as a state 

 of considerable effort and expenditure of 

 the sensitive and moving principle, by 

 the organs of our sensations and mo- 

 tions. This principle would soon have 

 been exhausted, if its reparation were 

 not facilitated by long intervals of rest. 

 Sleep and watching, therefore, call for 

 each other, and are of reciprocal neces- 

 sity. 



Sleep, however, only suspends that por- 

 tion of life, the design of which is to main- 

 tain a commerce with external objects 

 necessary to our existence. The interior, 

 or assimilating, functions are still carried 

 on. Digestion, absorption, circulation, 

 respiration, secretion, and nutrition, are 

 continued : the two former, indeed, seem 



to be performed with greater energy,, 

 while the rest are rather diminished. The 

 pulse is slower, respiration less frequent, 

 perspiration and urinary secretion less 

 abundant. 



Numerous causes of excitation con- 

 stantly acting on our senses during the 

 day, keep them in a state of activity , and 

 the absence of these at night is favour- 

 able to the repose of our organs. By 

 multiplying and increasing stimuli, the 

 period of repose may be put off; but these 

 gradually lose their powers, and after a 

 certain time, nothing can hinder its ap- 

 proach. Exhausted by fatigue and watch- 

 ing, the soldier sleeps at the side of the 

 cannon; the slave reposes under the 

 blows of his master ; and the criminal 

 sinks to rest amidst the agonies of tor- 

 ture. 



Sympathy. All parts of the living body 

 are united by certain relative connections, 

 namely, sympathies, which establish a 

 concord and harmony between the actions , 

 of the animal machine. The nature of 

 this phenomenon is still obscure : we know 

 not why, when one part is irritated, an- 

 other very distant organ should perceive 

 this irritation, and even contract ; nor are 

 we agreed on the peculiar instruments ef 

 sympathy, that is, on the organs which 

 connect two parts, one of which perceives 

 or acts while the other is affected. That 

 the nerves cannot be considered as the 

 exclusive means of it is obvious ; since 

 muscles, supplied from the same source 

 do not always sympathise, while a close 

 intercourse sometimes subsists between 

 parts whose nerves have no immediate 

 connection. Often, also, the sympathy is 

 not reciprocal. Examples of this princi- 

 ple may be seen in the swelling of the 

 breasts from distension of the ^ uterus; 

 itching of the nose from worms in the in- 

 testines, and of the glans penis from stone 

 in the bladder; contraction of the dia- 

 phragm from irritation of the pituitary 

 membrane ; pain in the shoulder from in- 

 flamed liver, &c. 



The chief; and perhaps most extensive 

 source of sympathy, must be referred to 

 the nerves, and particularly to a reaction 

 of the sensorium. When a part is stimu- 

 lated, and the sensorium affected by its 

 stimulation, the latter reacts through the 

 nerves on another organ, and incites it to 

 action, although there may be no imme- 

 diate nervous connection between them. 

 The motion of the iris, arising from the 

 impulse of light on the retina ; that of the 

 diaphragm in sneezing, from irritation of 

 the pituitary membrane, are examples, 





