332 ESSAYS anp OBSERVATIONS 
to thefe parts, does not produce its effects 
by entering the blood, and being, iby its 
means, conveyed to the brain, as fome 
have imagined, but by its immediate ac- 
tion on the organs and parts which it 
touches. N° 3. compared with N° 2. See. 
alfo Edinburgh Medical Effays, edit. 3. vol. 
5. part I. page 140. 
(d) Stnce, after decollation and the 
deftruction of the fpinal marrow, opium 
operates much more flowly in deftroying 
the heart’s motion in frogs, than it does 
when the animals are intire (N°.6, com- 
pared with N° 7.); it follows, that it muft 
produce its effects chiefly, if not wholly, 
by its action on the brain, {pinal marrow, 
and nervous fyftem. The heart of the 
frog N° 7. whofe brain and fpinal mar- 
row had been deftroyed, beat 27 times in 
a minute, after the animal had lain thirty 
fix minutes in a folution of opium 3 which 
was only three pulfations lefs than the 
heart of the frog N° 5. performed thirty 
five minutes after the deftrudction of its 
brain and fpinal marrow, although it was | 
not expofed to the action of opium. 
(¢) WHEN J 
