_Causes._ Age and good living, more particularly on highly albuminous food, may be adduced as the most prominent. Perhaps even more important are continued irritation in adjacent organs such as the rectum, bladder and urethra. It is the old, pampered dog that above all suffers from atonic, overloaded rectum, proctitis, piles, calculus, cystitis, and stricture, and the constant local pelvic congestion caused by one or other of these tends to a hyperplasia of the prostate. Again atheroma which is especially a disease of the aged is regarded as a cause of both cystitis and prostatic hypertrophy. Chronic inflammation in the prostate has been claimed as a factor, but contested on the ground that inflammation never increases normal growth though it may cause degeneration. The exudate of inflammation, tends, however, on its temporary arrest, to undergo organization, and such organization inclines to assume the structure which is normally built up by the adjacent trophic cells. The products of inflammation may, therefore, well contribute to hypertrophy, and above all to the increase of the simpler tissue represented by the fibrous framework of the gland. The congestion attendant on excessive venery has also been incriminated, and this too has been denied on the ground that the hypertrophy is not found in the young animals and men in which the generative ardor is greatest and most frequently aroused and gratified. Thompson’s idea is that the prostate, like the ovaries and womb, is especially prone to morbid growths and developments at the time when in advancing age, the normal generative functions are undergoing a rapid decline. The two conditions may well be recognized without considering them as mutually excluding each other as causative factors. _Lesions._ The enlargement is usually general, but it may predominate in the right, left or median lobe, the latter as a rule exercising greater compression of the urethra so that this is often marked in the worst cases. The hyperplasia may feel firm and resistant or it may be more or less soft from sacs of muco-purulent fluid imprisoned by the obstruction of the outlet canals. On the surface and on section the general appearance of the gland is pale, bloodless and uniformly solid. This comes from the great hypertrophy of the fibro-muscular stroma which has in many cases compressed the parenchymatous or secreting structure so as to cause its atrophy. The presence of calculi (mainly phosphatic) in the follicles is not uncommon.