GLANDS. 423 



The follicles cannot be exhibited separately as such, being 

 mere excavations or cells which exist in the substance of the 

 gland, and which are lined by prolongations of the mucous 

 membrane of the urethra. 



That the follicles constituting the essential structure of the 

 prostate gland are simply inversions of the genito-urinary 

 membrane, is proved by the fact that the epithelium which 

 lines them is of the clavate form, which has been elsewhere 

 described as appertaining to the bladder. 



In consequence of the large size of the follicles, and of the 

 fact of the epithelium which lines them forming on their in- 

 terior but a single arid even layer of cells, a considerable 

 space or cavity exists in the centre of each follicle. 



The tissue out of which the follicles are formed, and to the 

 presence of which the prostate owes much of its size and 

 nearly all its firmness, is a good example of the nucleated 

 variety of fibro-elastic tissue, approaching in its characters 

 very closely to the muscular fibre of organic life. 



The increase which so generally takes place in the size of 

 the prostate in old age is due to an increased development of 

 the above-named tissue. 



From the preceding description, it would appear that the 

 office of the prostate is simply to secrete mucus, and that it 

 does not, as has been conjectured, furnish any peculiar secre- 

 tion necessary, as some even have supposed, to fecundity. 



The most curious circumstance about the prostate is the 

 almost constant occurrence, in considerable numbers, of con- 

 cretions or calculi formed of concentric lamella?. These calculi 

 are situated in the follicles already described; they differ 

 from each other very greatly in size, form, and colour, and in 

 the number, arrangement, and strength of the concentric 

 capsules. Ordinarily, the concentric lamella) are disposed 

 around a single nucleus of granular and amorphous matter ; 

 sometimes, however, there are two or even three separate 

 nuclei within each calculus ; in these cases, each nucleus 

 will be encircled by its own lamella, the entire of them 

 being also included in a greater or less number of larger 

 lamella}. The form of the calculi, although various, has a 



