S UP. I. 16. 2. THEORY OF FEVlft. 499 



principally actuated by the sensorial powers of irritation, and of 

 association; but in some degree or at some times by those of sen- 

 sation, and even of volition. There are three kinds of stimulus, 

 which may easily be occasionally diminished, that of heat on the 

 skin, of food in the stomach, and of the oxygenous part of the at- 

 mosphere, which mixes with the blood in respiration, and stimu- 

 lates the heart and arteries. 



2. When any parts, which are naturally excited into perpetual 

 action by stimulus, become torpid or less active from decrease of 

 that stimulus; there first occurs a decrease of the activity of the 

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

 duces a torpor of the capillary vessels of the lungs, as is known 

 by the difficult respiration which immediately occurs; for, the 

 sensorial power of association, which naturally contributes to ac- 

 tuate the lungs, is now less excited by the decreased actions of 

 the cutaneous vessels, with which they are catenated. This con- 

 stitutes the cold fit of fever. 



There next occurs an accumulation of the sensorial power of 

 irritation in the parts, which were torpid from defect of stimulus, 

 as the cutaneous vessels for instance, when exposed to cold air; 

 and a similar accumulation of the sensorial power of association 

 occurs in the parts which were catenated with the former, as the 

 vessels of the lungs, in the example above mentioned. Whence 

 if the subduction of stimulus has not been too great, so as to im- 

 pair the health of the part, the activity of the irritative motions 

 returns, even though the stimulus continues less than usual; and 

 those of the associate motions become considerably increased, 

 because these latter are now excited by the previous fibrous mo- 

 tions, which now act as strong or stronger than formerly, and have 

 also acquired an accumulation of the sensorial power of associ- 

 ation. This accounts for the curious event of our becoming 

 warm in a minute or two after remaining in water of about 80 

 degrees of heat, as in the bath at Buxton; or in the cold air of a 

 frosty morning of about 30 degrees of heat. 



But if the parts thus possessed of the accumulated sensorial 

 powers of irritation and of association, be exposed again to their 

 natural quantity of stimulus, a great excess of activity supervenes; 

 because the fibres, which possess accumulated irritation, are now 

 excited by their usual quantity of stimulus; and those which pos- 

 sess accumulated association, are now excited by double or treble 

 the quantity of the preceding irritative fibrous motions, with 

 which they are catenated; this constitutes the hot fit of fever. 



Another important circumstance occurs, when the parts which 

 are torpid from decreased stimulus, do not accumulate a quantity 



