OF ANIMAL BODIES. 
103 
In sheep, the gastric fluid has no effect in digesting 
plants, unless they have been previously masticated. It only 
produces a slight maceration; nearly such as common wa¬ 
ter would produce, in a degree of heat somewhat exceed¬ 
ing the medium temperature of the atmosphere. But pro¬ 
vided that the plant has been reduced to pieces by chewing, 
the gastric juice then proceeds with it, first by softening its 
substance; next, by destroying its natural consistency; and, 
lastly, by dissolving it so completely, as not even to spare 
the toughest and most stringy parts, such as the nerves of 
the leaves. 
So far our accurate and indefatigable Abbe.—Dr. Ste¬ 
vens of Edinburgh, in 1777, found, by experiments tried 
with perforated balls, that the gastric juice of the sheep and 
the ox speedily dissolved vegetables, but made no impres¬ 
sion upon beef, mutton, and other animal bodies. Dr. Hun¬ 
ter discovered a property of this fluid, of a most curious 
kind; viz. that in the stomachs of animals which feed up¬ 
on flesh, irresistibly as this fluid acts upon animal substan¬ 
ces, it is only upon the dead substance, that it operates at 
all. The living fibre suffers no injury from lying in con¬ 
tact with it. Worms and insects are found alive in the 
stomachs of such animals. The coats of the human stom¬ 
ach, in a healthy state, are insensible to its presence: yet, 
in cases of sudden death, (wherein the gastric juice, not 
having been weakened by disease, retains its activity,) it 
has been known to eat a hole through the bowel which con¬ 
tains it. # How nice is this discrimination of action, yet 
how necessary? 
But to return to our hydraulics. 
III. The gall-bladder is a very remarkable contrivance. 
It is the reservoir of a canal. [PI. XVIII. fig. 1, 2.] It 
does not form the channel itself, i. e. the direct communi¬ 
cation between the liver and the intestine which is by an¬ 
other passage, viz. the ductus hepaticus, continued under 
the name of the ductus communis; but it lies adjacent to 
this channel, joining it by a duct of its own, the ductus 
cysticus; by which structure it is enabled, as occasion 
may require, to add its contents to, and increase the flow 
of bile into the duodenum. And the position of the gall¬ 
bladder is such as to apply this structure to the best advan¬ 
tage. In its natural situation, it touches the exterior sur¬ 
face of the stomach* and consequently is compressed by the 
distension of that vessel: the effect of which compression 
* Phil. Trans, vol. Ixii. p. 447. 
