CH. XLIII.] FEVER 641 



does the temperature at once fall, but the animal becomes poikilo- 

 thermic. 



The seat of the heat-regulating mechanism in the brain is a 

 matter of much uncertainty. It is possibly in the basal ganglia of 

 the cerebrum, or in this neighbourhood. 



Fever. Diseases may cause the temperature to vary considerably, 

 especially those which we term febrile. 



A mere increase in the production of heat does not necessarily 

 cause fever. The administration of food causes increased combustion 

 in the body ; but there is no rise of temperature in health, because 

 pari passu with the increased production there is increased loss of 

 heat. Similarly, diminution in the loss of heat, such as occurs on a 

 hot as compared with a cold day, does not produce fever, because the 

 production of heat within the body is correspondingly diminished. 

 A febrile condition may, however, occur if tight-fitting and otherwise 

 unsuitable clothing which interferes with the proper action of the 

 skin is worn in hot weather ; this is the frequent cause of " heat- 

 stroke " among soldiers in the tropics. 



In fever there is increased production of heat, as is shown by 

 metabolic balance-sheets; the intake of food is usually small, and 

 the discharge of carbon, nitrogen, etc., results mainly from tissue 

 disintegration ; this is even greater than in ordinary inanition ; the 

 tissues are said to be in a " labile " condition, that is, they are easily 

 broken down. Usually the skin is dry, the sweat-glands, like most 

 of the secretory glands, being comparatively inactive, and so the 

 discharge of heat is lessened. The skin, however, may sometimes be 

 bathed in perspiration and yet high fever be present. The essential 

 cause of the high temperature in fever is neither increased formation 

 nor diminished discharge of heat, but an interference with the 

 mechanism which in health operates so as to equalise the two. 



The Action of Drugs. From what has been said, it will be evident 

 that drugs may reduce fever in more than one way : for instance, 

 they may reduce the metabolism of the muscles, e.g. quinine ; they 

 may cause increased heat loss by promoting perspiration and 

 vascular dilatation in the skin, e.g. pilocarpine ; or they may act on 

 the central heat-regulating mechanism (corpus striatum ?), e.g. phen- 

 acetin. 



2 s 



