RECEPTACLES FOR SECRETED PRODUCTS. 
303 
happens most frequently in regard to the important Excretions, 
as if Nature had especially provided for their continued sepa¬ 
ration from the blood, that its purity may be unceasingly 
maintained. Thus the urinary secretion has been passed off 
from the surfaces of the skin, stomach, intestines, and nasal 
cavity, and also from the mammary gland; the colouring 
matter of the bile, when it accumulates in the blood (as in 
jaundice), is separated from it in the skin and conjunctival 
membrane of the eye (§ 537); and milk has been poured 
forth from pustules on the skin, and from the salivary glands, 
kidneys, &c. Such cases have been regarded as fabulous ; 
but they rest upon good authority, and they are quite consistent 
with physiological principles. 
362. Some of the main ducts or channels, through which 
the glands pour forth their secretions, are provided with 
enlargements or receptacles, which serve to retain and store 
up the fluid for a time, until it may be desirable or convenient 
that it should be discharged. Thus, in most of the higher 
animals, the duct which conveys into the intestinal tube the 
bile secreted by the liver, is also connected with a receptacle 
termed the gall-bladder ; the bile, as it is secreted, passes into 
this, and is retained there until it is 
wanted for assisting in the digestive 
process (§ 213); when it is pressed out 
into the intestinal canal. It is a curious 
fact, that in most persons who die of 
starvation, the gall-bladder is found, dis¬ 
tended with bile; showing that the 
secretion has continued, although it has 
not been poured into the intestine for 
want of the stimulus occasioned by the 
presence of food in the latter. In many 
quadrupeds, especially those of the 
Buminant tribe, the milk-ducts are in 
like manner dilated into a large re¬ 
ceptacle, the udder, which retains the 
secretion as it is formed, until the 
period when it is needed. In all Mammals, and in some 
Beptiles, Mollusks, and Insects, but not in Birds or Fishes, 
we find the ureters , which convey away the urinary excretion 
from the kidneys, dilated at their lower extremity into a 
Fig. 168. —Urinary Ap¬ 
paratus. ' 
a, kidneys ; b, ureters; c, 
bladder; d, its canal, the 
urethra. 
