SECT. XXXIII. a. DISEASES OF SEMSATION. 453 



5. It would appear, that the vafcular fyftem of 

 other animals are lefs liable to be put into action 

 by their general fum of pleafurable or painfui fen- 

 fation ; and that the trains of their ideas, and the 

 mufcular motions uiually aflbciated with them, are 

 lefs powerfully conneded than in the human fyitem. 

 For other animals neither weep, nor fmile, nor 

 Jaugh ; and are hence feldom fubjeft to delirium,, 

 as treated of in Sed}. XVI. on InftincL Now as 

 pur epidemic and contagions djfeafes are probably 

 produced by difagreeable feafatiou, and not fimply 

 by irritation ; there appears a reafon, why brute 

 animals are lefs liable to epidemic or contagious 

 difeafes; and fecondiy, why none of our contagions, 

 as the fmall-pox or meafles, can be communicated 

 to them, though oae of theirs, viz. the hydropho- 

 bia, as well as many of their poifons, as thofe of 

 foakes and of infe&s, cornmunjcate tbeir Deleterious 

 or painful effedls to mankind- 



Where the quantity of general painful fenfation 

 is too great in the fyftem, inordinate voluntary ex- 

 ertions are produced either of pur ideas, as in me- 

 lancholy and madnefs, or of our mufcles, as iu 

 convulfion. From thefe maladies alfo brute animals 

 are much more exempt than mankind, owing to 

 their greater inaptitude to voluntary exertion, as 

 mentioned in Seel. XVI. on Inftincl. 



IL i. When any moving organ is excited into 

 fuch violent motions, that a quantity of pleafurable 

 pr painful fenfation is produced, it frequently hap- 

 pens (but not always) that new motions of the af- 

 fefted organ are generated in confequence of the 

 pain or pleafure, which are termed inflammation. 



Thefe new motions are of a peculiar kind, tend- 

 ing to diflend the old, and to produce new fibres, 

 and thence to elongate the ftraight mufcles, which 

 ferve locomotion, and to form new veflels at the 

 extremities or fides of the vafcular mufcles. 



2. Thus 



