t^HYSlCAL AND LITERARY. 311 



their nerves, as we have elfe where endea- 

 voured to (hew *, 'tis eafy to fee that opium 

 muft, by deftroying the fenfibility of the 

 mufcles, of confequence alfo deftroy their 

 irritability. 



(u) In animals which have got a large 

 dofe of opium^ the veins, efpecially thofe of 

 the membranes of the brain, are obferved 

 to be much fwelled j whence it has been 

 thought, that opium produces its efFe(5ls in 

 the bodies of animals, partly, at leaft, by 

 rarefying the blood and compreffing the 

 brain : but this difteniion of the veins feems 

 to be no more than a confequence of the ve- 

 ry flow motion of the blood through the 

 heart, on account of the infenfibility with 

 which this organ is affedted -f*. 



(v) Since opium foon puts a ftop to the 



vital motions of animals, which yet continue 



Vol. IL R r in 



* Eflay on the vital and other involuntary motions of a- 

 nimals, feft. ix. and Phyfiological Effays, p. i88, &c. 



-|- In frogs, into whofe ftomach and guts I had injefted 

 a folution of opium, I not only found the heart's auricle, 

 but alfo the great veins leading to it, much diftended with 

 blood. Vid. Effay on vital motions, &c. p. 371. anA 

 373. 



