SECT. XXXIII. i. 5. OF SENSATION. 309 



to external objefts, neither of which exifts in the delirium of 

 fevers or in dreams. 



5. It would appear, that the vafcular fyftems of other animals 

 are lefs liable to be put into aHon by their general fum of 

 pleafurable or painful fenfation ; and that the trains of their 

 ideas, and the mufcular motions ufually aflbciated with them, 

 are lefs powerfully conne&ed than in the human fyftem. For 

 other animals neither weep, nor fmile, nor laugh ; and are 

 hence feldom fubjeft to delirium, as treated of in Se6i. XVI. on 

 Inftinft. Now as our epidemic and contagious difeafes are 

 probably produced by difagreeable fenfation, and not fimply by 

 irritation ; there appears a reafon why brute animals are lefs li- 

 able to epidemic or contagious difeafes ; and fecondly, why none 

 of our contagions, as the fmall-pox or meafles, can be communi- 

 cated to them, though one of theirs, viz. the hydrophobia, as 

 well as many of their poifons, as thofe of fnakes and of infefts, 

 communicate their deleterious or painful effeftsto mankind. 



Where the quantity of general painful fenfation is too great 

 in the fyftem, inordinate voluntary exertions are produced either 

 of our ideas, as in melancholy and madnefs, or of our mufcles, 

 as in convulfion. From thefe maladies alfo brute animals are 

 much more exempt than mankind, owing to their greater inapti- 

 tude to voluntary exertion, as mentioned inSe&.XVI.on Inftinft. 



II. i. When any moving organ is excited into iuch violent 

 motions, that a quantity of pleafurable or painful fenfation is 

 produced, it frequently happens (but not always) that new mo- 

 tions of the affected organ are generated in confequence of the 

 pain or pleafure, which are termed inflammation. 



Thefe new motions are of a peculiar kind, tending to diftend 

 the old, and to produce new fibres, and thence to elongate the 

 flraight mufcles, which ferve locomotion, and to form new vef- 

 fels at the extremities or fides of the vafcular mufcles. 



2. Thus the pleafurable fenfations produce an enlargement of 

 the nipples of nurfes, of the papillae of the tongue, of the penis, 

 and probably produce the growth of the body from its embryon 

 (tare to its maturity ; whilft the new motions in confequence of 

 painful fenfation, with the growth of the fibres or veflels, which 

 they occafion, are termed inflammation. 



Hence when the ftraight mufcles are inflamed, part of their 

 tendons at each extremity gain new life and fenfibility, and thus 

 the mufcle is for a time elongated ; and inflamed bones become 

 fofr, vafcular, and fenfible. Thus new veflels (hoot over the 

 cornea of inflamed eyes, and into fcirrhous tumours, when they 

 become inflamed ; and hence all inflamed parts grow together 

 by intermixture, arid inofculation of the new and old veflels, 



The 



