OF THE GALL-BLADDER. 157 



dilution of the bile in the duodenum ; and, as the contents are absorbed, 

 the bile becomes less and less diluted, so that it becomes more and 

 more apparent ; and, as it becomes less diluted, it, of course, acts more 

 as a stimulant to the last intestines. 



These circumstances are plainly seen in some animals whose bile is 

 of a bright or high green colour, and which have a large quantity ; for 

 in them the contents of the upper part of the intestines are only a little 

 tinged, but those of the lower part are of a strong colour. This is still 

 better seen in those animals that have fasted long, where the bile is 

 but little diluted. Bile is, I should suppose, bitter in insects, but not 

 in the oyster, muscle, lobster, &c. This last circumstance is a strong 

 proof that the bile is not digested and absorbed ; for in very hungry 

 animals we should not expect to see anything in the state of bile in the 

 intestines, if the bile went through the stomachic digestion. 



If the bile is intended as a natural purge, and as many animals 

 regiirgitate the excrementitious part of their food, the question suggests 

 itself, Is bile necessary for regurgitation, and have those animals bile ? 

 We can regurgitate without bile, and many birds regurgitate part of 

 their indigestible food without bile. Therefore probably all those 

 animals which do regurgitate their excrementitious parts \_Medusce, 

 Actinias] have nothing analogous to liver and bile, but only those ani- 

 mals that have intestines. 



We often find gall-stones transparent. Is this the salts of the bile 

 crystallized ? 



On the Gall-bladder. 



Some animals have gall-bladders and some have them not. Those 

 that have a gall-bladder, must have part of the bile passing into the 

 gall-bladder, and the other part into the gut at all times. Those that 

 have no gall-bladder, must have the bile always passing into the gait. 

 This difference arises from two circumstances ; the first is, that the bile 

 which is constantly used must be thin ; and bile that is only used 

 at certain times is required to be thick. 



Now it would appear that some animals require bile equally at all 

 times ; therefore they have a constant supply of bile, which is thin. 

 There are other animals which seem to require bile, but more at one 

 time than at another ; the bile which they are constantly in want of is 

 thin, whereas the other is thick. 



Now if this were not the case, Nature could easily have made it 

 otherwise ; for instance, if that bile which is always wanted by right 

 should be thick, then Nature could have placed a bladder in the middle 

 of the duct, which would have served as a reservoir, where it might 



