$ect. XXXII. 2. 3. OF IRRITATION. 28- 



The former circumftance needs no illuftration ; fince if the (limit- 

 lus of the blood, or the irritability of the Sanguiferous fyftem be 

 increased, and the ftrength of the patient not diminihed, it is 

 plain that the .motions mud be performed quicker and ftronger. 

 In the latter eircumflance the weakneis of the mufcular pow- 

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

 coats of the arteries, which they poflefs befides a mufcular power 

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

 their ufual diameters. The heart being thus flopped, when it 

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

 teries being dilated to lek than their ufual diameters, begin h 

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

 ftages 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 

 118 or 120 pulfation s in a minute. It mult be added, that in 

 thefe cafes, while the puife is very fmali 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 riot 

 completely empty itfeif. 



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

 animals which are bleeding to death in the fiaughter-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 mult contract fooner, or more frequently, 

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

 tity of blood, this caufe may occasionally 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 fenforial 

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

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

 age or by drunkenifefs. See Seel. XII. j. 4. XII. 3. 4. 



It may neverthelefs frequently happen, that both the deficiency 

 of ftimuius, as where the quantity of blood is leflened (as de- 

 scribed in No. 4. of this feclion), and the deficiency of fenforial 

 power, as in thofe of the temperament'of inirritabilty, delcribed 

 in Sect. XXXI. occur at the fame time j which will thus add 

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



III. 1. A certain degree of heat is necellary to mufcular mo- 

 tion, and is, in confequence, effential to life. This is obferved 

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

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

 riecefiary ftimuius of heat has two fources \ one from the fluid 



atmofphere 



