104 OF THE VESSELb- 



f 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 stomach 

 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 contains 

 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 intestines, which is by an- 

 other passage, viz. the ductus hepaticus, continued under 

 the nan^e 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 occasions 

 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 

 is, to force out from the bag, and send into the duodenum, 

 an extraordinary quantity of bile, to meet the extraordinary 

 demand which the repletion of the stomach by food is about 

 to occasion.! Cheselden describes"! the gall bladder as seated 

 against the duodenum, and thereby liable to have its fluid 

 pressed out, by the passage of the aliment through that cav- 

 ity ; which likewise will have the effect of causing it to' be 

 received into the intestine, at a right time, and in a due 

 proportion. 



^ Phil. Trans, vol. Ixii. p, 447. t Keill's Anat. p. 64. 

 I Anat. p. 164. 



