FEVERS. 497 



(XXXV.), but particularly from symptoms which are peculiar 

 to the brain itself. Delirium is a frequent symptom of fever ; 

 and as from the Physiology and Pathology we learn that this 

 symptom commonly depends upon some inequality in the ex- 

 citement of the brain or intellectual organ (See Physiology, p. 

 146.), we hence conclude, that in fever it denotes some di- 

 minution in the energy of the brain. Delirium, indeed, seems 

 often to depend upon an increased impetus of the blood in the 

 vessels of the brain, and therefore attends phrenitis. It fre- 

 quently appears also in the hot stage of fevers, accompanied 

 with a headach and throbbing of the temples. But as the im- 

 petus of the blood in the vessels of the head is often considera- 

 bly increased by exercise, external heat, passions, and other 

 causes, without occasioning any delirium, so, supposing that the 

 same impetus in the case of fever produces delirium, the reason 

 must be, that at the same time there is some cause which di- 

 minishes the energy of the brain, and prevents a free commu- 

 nication between the parts concerned in the intellectual func- 

 tions. Upon the same principles, also, I suppose there is 

 another species of delirium, depending more entirely on the di- 

 minished energy of the brain, and which may therefore arise 

 when there is no unusual increase of the impetus of the blood 

 in the vessels of the brain. Such seems to be the delirium oc- 

 curring at the beginning of the cold stage of fevers, or in the 

 hot stage of such fevers as shew strong marks of debility in the 

 whole system. 



" I have observed, that in the hot fit of an intermittent a deli- 

 rium frequently arises, and that then it is attended with head- 

 ach and throbbing of the temples, and with a full and strong 

 pulse ; here we do not at all hesitate in ascribing the delir- 

 ium to the increased impetus of the blood in the vessels of 

 the brain ; and we know that persons have been freed from it by 

 raising their head a little higher, and even by changing sides 

 the headach and delirium have been found sensibly to abate ; 

 besides, every inflammation of the brain consists in such an in- 

 creased impetus, and is constantly accompanied with increased 

 delirium. So there is no doubt that one species of delirium 

 depends upon an increased action of the vessels of the brain. 

 " But pathologists have gone too far, and supposed this to 



