Sup. I. 16. 2. THEORY OF FEVER. 49 y 



principally actuated by the fenforial powers of irritation, and of 

 affociation •, but in fome degree or at fome times by thofe of 

 feniation, and even of volition. There are three kinds of ftim- 

 ulus, which may eafily be occafionally diminifhed, that of heat 

 on the fkin, of food in the ftomach, and of the oxygenous part 

 of the atmoiphere, which mixes with the blood in refpiration, 

 and ftimulates the heart and arteries. 



2. When any parts, which are naturally excited into perpetu- 

 al action by ftimulus, become torpid or lefs active from decreafe 

 of that ftimulus ; there fir ft occurs a decreafe of the activity of 

 the parts next catenated with them ; thus going into cold water, 

 produces a torpor of the capillary veffels of the lungs, as is 

 known by the difficult refpiration, which immediately occurs ; 

 for the fenforial power of affociation, which naturally contributes 

 to actuate the lungs, is now lefs excited by the decreafed actions 

 of the cutaneous velTels, with which they are catenated. This 

 constitutes the cold fit of fever. 



There next occurs an accumulation of the fenforial power of 

 irritation in the parts, which were torpid from defect of ftimu- 

 lus, as the cutaneous veffels for inftance when expofed to cold 

 air ; and a fimilar accumulation of the fenforial power of affo- 

 ciation occurs in the parts which were catenated with the for- 

 mer, as the veffels of the lungs in the example above mentioned. 

 Whence, if the fubduclion of ftimulus has not been too great, 

 fo as to impair the health of the part, the activity of the irrita- 

 tive motions returns, even though the ftimulus continues lets 

 than ulual ; and thofe of the affociate motions become confid- 

 erably increafed, becaule thefe latter are now excited by the pre- 

 vious fibrous motions, which now act as ftrong or ftronger than 

 formerly, and have alfo acquired an accumulation of the fenfo- 

 rial power of affociation. This accounts for the curious event 

 of our becoming warm in a minute or two after remaining in 

 v/ater of about 80 degrees of heat, as in the bath at Buxton ; or 

 in the cold air of a frofty morning of about 30 degrees oi heat. 



But if the parts thus poileffed of the accumulated fenforial 

 powers of irritation and of affociation be expofed again to their 

 natural quantity of ftimulus, a great excels of activity fuper- 

 venes j becaufe the fibres, which poffefs accumulated irritation, 

 are now excited by their uiual quantity of ftimulus ; and thole 

 which poffefs accumulated affociation, are now excited by double 

 or treble the quantity of the preceding irritative fibrous mo- 

 tions, with which they are catenated •, this conftitutes the hot 

 fit of fever. 



Another important circumftance occurs, when the parts, 

 which are torpid from decreased ftimulus, do not accumulate a 



quantity 



