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sics, or psychology, of analysis of the understanding, but better described 

 by that applied to it by the writers of our days, ideology. On this sci- 

 ence, you may consult with advantage, the philosophical works of Plato 

 and Aristotle, among the ancients ; of Bacon, Hobbes, Locke, Condillac, 

 Bonnet, Smith, Reid, Dugald, Stewart, Brown, Cabanis, and. Tracy, 

 among the moderns. 



CLX. Of sleep and waking. The causes of excitation to which our 

 organs are exposed during waking, tend to increase progressively their 

 action ; the pulsations of the heart, for instance, are much more frequent 

 in the evening than in the morning, and this motion, gradually accelera- 

 ted, would soon be carried to a degree of activity incompatible with the 

 continuance of life, did not sleep daily temper this energy, and bring it 

 down to its due measure. Fever is occasioned by long continued want of 

 sleep, and in all acute diseases, the exacerbation comes on towards even- 

 ing, the night's sleep abates again the high excitation of power: but this 

 state of the animal economy, so salutary and so desirable in all sthenic 

 affections, is more injurious than useful in diseases, consisting chiefly in 

 extreme debility. Adynamy shows itself, almost always, in the morning,in 

 putrid fevers ; and petechiae, a symptom of extreme weakness, break out 

 during sleep. This state is, likewise favourable to the coining on and to 

 the progress of gangrene, and this is a pathological fact well ascertained. 

 In all the cases I have mentioned, sleep does not improve the condition 

 of the patients ; a thing easy to conceive, since it only adds to accidental 

 debility, the essential characteristic of the disease, weakness which is al- 

 so its principal characteristic. 



Sleep, that momentary interruption in the communication of the senses 

 with outward objects, may be defined the repose of the organs of sense, 

 and of voluntary motion. During sleep, the inward or assimilating func- 

 tions are going on : digestion, absorption, circulation, respiration, secre- 

 tion, nutrition, are carried on; some as absorption and nutrition* with 

 more energy than during waking, whilst others are evidently slackened. 

 During sleep, the pulse is slower and weaker, inspiration is less frequent, 

 insensible perspiration, urine, and all other humours derived from the 

 blood, are separated in smaller quantity. Absorption is, on the contra- 

 ry, very active : hence the danger of falling asleep inithe midst of a noxi- 

 ous air. It is known that the marshy effluvia, which make the Com- 

 pagna di Roma so unhealthy, bring on, almost inevitably, intermittent 

 tevers, when the night is passed there, whilst travellers, who go through 

 without stopping, are not affected by itf. 



* Nutrition is evidently more active during 1 sleep, in early life, especially in childhood; 

 and, in many constitutions and habits of body, it appears equally active, during this 

 state, through the middle stages of life ; but as soon as the period of decay approaches, 

 absorption appears to predominate, while on the contrary, nutrition gradually languishes 

 more and more, during sleep, as age advances. In the middle periods of existence it is 

 difficult to determine whether absorption or nutrition is augmented during this state : 

 the difference cannot always be correctly appreciated ; but we generally find that when 

 the one is increased the other is generally diminished, both functions being seldom aug- 

 mented or impaired at the same time. Copland. 



f Tins is quite as much the result of the low state of the nervous and vital energies 

 of the system during sleep. The vital powers at that time are not under the impression 

 of the excitements communicated through the medium of the nerves of sensation and 

 motion ; the operations, indeed, of this part of the nervous system are for a time suspend- 

 ed, and consequently the vital functions lose part of their energy, and are open to the 



