PHYSIOLOGY. 141 



mina; upon the state of the simple solid (XIV. XXIV.); 

 upon exercise ; upon the temperature to which men and o- 

 ther animals are accustomed, a degree of heat approaching to 

 excess, relaxing and weakening the system, whereas a certain 

 degree of cold invigorates and strengthens it ; upon a certain 

 proportion of blood vessels in the system, and a fullness and 

 tension of the blood vessels of the brain ; and, lastly, upon 

 certain stimulating powers, diet and wine, which produce more 

 vigorous contraction. 



" The causes of debility of the brain are the converse of the 

 causes of increased vigour now mentioned, viz. indolence, the 

 excesses of heat and of cold, want of nourishment and evacua- 

 tions, which diminish the state of tension in the whole system, 

 and the absence of the usual stimuli. Where stimuli have 

 been daily applied, as in the case of wine, the system comes to 

 depend upon them for the degree of its tension : their absence 

 therefore induces debility. Thus, in a person who has used the 

 habitual stimulus of a dram, when that stimulus should be re- 

 newed a sense of debility, a tremor occurs, till the tension is 

 again occasioned by the application of a dram to the stomach. 

 There are causes of collapse also, such as certain sedatives, or 

 as we call them poisons, which in like manner induce debility. 

 Thus, a man intoxicated with wine or opium, has not his usual 

 vigour, and though the quantity may not be sufficient to kill 

 him, it leaves the body under a considerable degree of debility. 

 I could add here the causes of fatigue, although I cannot ex- 

 plain them (CXIII.), We may, perhaps, find a solution in 

 this, that every unusual degree of excitement is followed by a 

 like degree of collapse, and that these states induce one another 

 (CXXX.). This leads to an important question in Pathology, 

 viz. how the debility in fevers is occasioned, and how it it is con- 

 tinued ? It may be referred to the head of poisons acting as 

 sedatives ; and many circumstances lead to this supposition ; 

 but the most pure inflammatory fevers, produced without any 

 concurring contagion by the operation of cold, leave a state of 

 debility subsisting in the system, in proportion to the degree of 

 the fever, for a long time afterwards : and where contagion has 

 been introduced as the first cause of debility, when this has 

 been seemingly removed, and its symptoms have passed away, 



