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 

 Euminant tribe, the milk-ducts are in 

 a, kidneys; 6, ureters; e , ^ke manner dilated into a large re- 

 hiadder ; d, its canal, the ceptacle, the udder, which retains the 



urethra. , . .!_/ i . -i .-i 



secretion as it is formed, until the 

 period when it is needed. In all Mammals, and in some 

 Eeptiles, 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. 



