SECT. XXXII. 2- 3. OF IRRITATION. 285 



The former circumflance needs no ill uftration ; fince if the ftirnu- 

 ] us of the blood, or the irritability of the fanguiferous fyftem be 

 mcreafed, and the ftrength of the patient not diminifhed, it is 

 plain that the motions muft be performed quicker and ftronger. 



In the latter circumftance the weaknefs of the mufcular pow- 

 er of the heart is foon over- balanced by the elafticity of the 

 coats of the arteries, which they pofiefs befides a muicular power 

 of contraction ; and hence the arteries are diftended to lefs than 

 their ufual diameters. The heart being thus (topped, when at 

 is but half emptied, begins fooner to dilate again ; and the ar- 

 teries being dilated to lefs than their ufual diameters, begin fo 

 much fooner to contract themfelves ; infomuch, that in the laft 

 fbges of fevers with weaknefs the frequency of pulfation of the 

 heart and arteries become doubled ; which, however, is never 

 the cafe in fevers with ftrength, in which they feldom exceed 

 1 1 8 or 1 20 pulfarions in a minute. It muft be added, that in 

 thefe cafes, while the pulfe is very fmall and very quick, the- 

 heart often feels large, and labouring to one's hand , which co- 

 incides with the above explanation, (hewing that it does not 

 completely empty itfelf. 



3. In cafes however of debility from paucity of blood, as in 

 animals which are bleeding to death in the flaughter-houfe, the 

 quick pulfations of the heart and arteries may be owing to their 

 not being diftended to more than half their ufual diaftole ; and 

 in confequence they muft contract fooner, or more frequently, 

 in a given time. As weak people are liable to a deficient quan- 

 tity of blood, this caufe may occafionally contribute to quicken 

 the pulfe in fevers with debility, which may be known by ap- 

 plying one's hand upon the heart as above ; but the principal 

 caufe I fuppofe to confift in the diminution of fenforial power. 

 When a mufcle contains, or is fupplied with but little fenforiai 

 power, its contraction foon ceafes, and in confequence may foon 

 recur, as is feen in the trembling hands of people weakened by 

 age or by drunkennefs. See Seel. XII. i 4 XII. 3. 4, 



It may neverthelefs frequently happen, that both the deficiency 

 of ftimulus, as where the quantity of blood is lefiened (as de- 

 fcribed in No. 4. of this feclion), and the deficiency of fenforiai 

 power, as in thofe of the temperament of inirritability, defcribed 

 in Se6t XKXI. occur at the fame time ; which will thus add 

 to the quicknefs of the pulfe and to the danger of the difeafe. 



III. i . A certain degree of heat is neceflary to mufcular mo- 

 tion, -and is, in cor.fequence, efiential to life. This is obferved 

 in thofe animals and infetls which pafs the cold feafon in a tor- 

 pid (late, and which revive on being warmed by the fire. This 

 n. eceffcry ftimulus of heat has two fources ; one from the fluid 



atmofphere 



