‘ 
_ blood through the heart, on account of 
PHYSICAL anp LITERARY. 343 
nor be conceived to alter the nature of 
their gluten; fhew, that the irritability 
ofthe mufcles has not its feat in this 
glue, as fome have lately imagined *. 
But, if the motions of irritated mu(cles 
be owing to a difagreeable fenfation ex- 
cited in them or their nerves, as we have 
elfewhere endeavoured to fhew f, it is eafy 
to fee, that opium mutt, by deftroying . 
the fenfibility of the mufcles, of confe- 
quence 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 ob- 
ferved to be much {welled ; whence it has 
been thought, that opium produces its ef- 
fects in the bodies of animals, partly, at 
leaft, by rarefying the blood and com- 
preffing the brain: But this diftenfion of 
the veins feem to be no more than a con- 
fequence of the very flow motion of the 
the 
* A&, Gotting, vol..2. p, 152s 
_ + Effay on the vital and other involuntary motions of 
animals, fect, ix, and Phyfiological Effays, p. 188. &c. 
