SECT. XII. 5. 2. AND EXERTION. 65 



natural in one part of the fyftem, is liable to produce an increafe 

 of the exertion of it in fome other part. Thus by the action of 

 vomiting, in which the natural exertion of the motions of the 

 ftomach are deftroyed or diminifhed, an increafed abforption of 

 the pulmonary and cellular lymphatics is produced, as is known 

 by the increafed abforption of the fluid depofited in them in 

 dropfical cafes. But thefe partial quiefcences of fenforial power 

 are alfo fometimes attended with other partial quiefcences, which 

 fympathize with them, as cold and pale extremities from hun- 

 ger. Thefe therefore are to be afcribed to the afibciations of 

 fympathy explained in Seel:. XXXV. and not to the general 

 accumulation of fenforial power. 



2. A quantity of ftimulus lefs than natural, applied to fibres 

 previoufly accuftomed to perpetual ftimulus, is fucceetied by ac- 

 cumulation of fenforial power in the affected organ. The truth 

 of this propofition is evinced, becaufe a ftimulus lefs than nat- 

 ural, if it be fomewhat greater than that above mentioned, will 

 excite the organ fo circumftanced into violent activity. Thus 

 on a frofty day with wind, the face of a perfon expofed to the 

 wind is at firft pale anc^ fhrunk j but on turning the face from 

 the wind, it becomes foon of a glow with warmth and flushing. 

 The glpw of the fkin in emerging from the cold-bath is owing 

 to the fame cauie. 



It does not appear, that an accumulation of fenforial power 

 above the natural quantity is acquired by thofe mufcles, which 

 are not fubject to perpetual ftimulus, as the locomotive mufcles ; 

 thefe, after the greateft fatigue, oniy acquire by reft their uiual 

 aptitude to motion ; whereas the vafcular fyftem, as the heart 

 and arteries, after a (horr quiefcence are thrown into a violent ac- 

 tion by their natural quantity of ftimulus. 



Neverthelefs by this accumulation of fenforial power during 

 the application of decreafed ftimulus, and by the exhauftion of 

 it during the action of increafed Itimuius, it is wifely provided, 

 that the actions of the vafcular mufcles and organs of fenfe are 

 not much deranged by fmali variations of (timuius ; as the quan- 

 tity of fenforial power becomes in fome meafure inverfely as the 

 quantity of ftimulus. 



3. A quantity of ftimulus lefs than that mentioned above, and 

 continued for fome time, induces pain in the affected organ, as 

 the pain of cold in the hands, when they are immerfed in fnow, 

 is owing to a deficiency of the ftimulation of heat. Hunger is 

 ii pain from the deficiency of the ftimulation of food. Pain 

 in the back at the commencement of ague-fits, and the head- 

 achs which attend feeble people, are pains from defect of ftirn- 

 wins, and are hence relieved by opium, cfTential oils, fpirit of wine. 

 VOL. I. K ' As 



