Prostatic Calculi.—It is most probable that these concretions undergo an early solution ; thus yielding up their granular or amorphous contents to form a part of the secretion of the gland. This is the opinion of Dr. Jones. But if they are not removed in this manner they become the nuclei of prostatic calculi.
Prostatic calculi are thus formed in the gland, occasionally in immense numbers ; they are generally rounded in form, and frotn their pearly semi-transparent appearance, Dr. Wollaston compared them to grains of pearl barley. They become covered with a brownish coating from a deposit from the natural secre tion of' the gland. Continuing to increase in size, they come in contact with one another, and at the points of contact are as it were articulated together. They are smooth upon the surface, and often resemble porcelain from the high polish they obtain. As they increase still further in size they cause absorption of the surrounding glandular substance, and thus convert the gland into a multilocular bag, in which as many as fifty or sixty calculi have been seen. In this condition, if the finger is passed per anum, the prostate gives the feel of a bag of marbles. Sometimes there is only s! single large cavity in one lobe filled with a single calculus. The smaller stones often escape into the bladder through the dilated ducts,and are readily extracted by the urethral forceps. When divided they exhibit a radiated and laminated structure; or they are com pact.
From the analysis which has been made of the prostatic calculi in the College of Surgeons, it appears that the relative proportion of phosphoric acid and lime in all the varieties of these calculi appears to vary considerably, although they may, in all probability, be re duced to two salts, — the neutral phosphate of lime, or the diphosphate, which exists in those varieties that are partially fusible before the blowpipe, and which generally exhibit a crystalline structure; and the basic phosphate of lime which is completely infusible by the mouth of the blowpipe. In estimating the fusi bility of these compounds, care must be taken that none of the triple phosphate is present.* When they pass into the bladder, they excite irritation of its mucous surface, and become coated with the triple phosphate; or if a large stone remains in the prostatic portion of the urethra, it may cause a deposit of lithic acid on its surface from the urine which is conti nually passing over it. A single calculus sometimes extends from the prostate into the membranous part of the urethra, which be comes inuch dilated. In these cases the cal culus has usually an elongated, somewhat conical figure, and consists of two or three separate portions, which are closely adapted to each other, and have polished articulating surfaces at the point of contact. The rounded extremity of one calculus is often received into a corresponding concavity of another. These calculi almost always contain a larger portion of phosphate and carbonate of lime, than those found in any other situation. When the prostate is completely disorganised and converted into a mere cyst, the calculi found in its cavity are of the fusible character, or contain more or less of the triple phosphates.
It sometimes happens that the phosphates are secreted by the prostate in immense quan tities, and are excreted with the urine, giving it a milky aspect. This may be confounded with a sunilar deposit from the urine itself, but it is generally accompanied by symptoms of irritation of the prostate gland and neck of the bladder — as discharge from the urethra ; hence the diagnosis is not difficult.
" Vogel, in his pathological anatomy of the human body, has given an account of these prostatic calculi : he described them of small size, not larger than a pin's head, and usually of a brownish, reddish-brown, or. yellowish-brown colour, presenting a crystalline or laminated arrangement, with a polyhedric or facetted surface. He says that they are formed by a precipitate of phosphate of " Lassaigne has given an analysis of the quantitative composition of these concretions. Thus in 100 parts there are contained Basic phosphate of lime . . 84.5 Carbonate of lime . . . 0.5 Animal matter (mucus, &c.) . 15.0 It is presumed that they are formed by a de position of these salts when existing in excess in the prostatic secretion. Similar concre tions are occasionally met with in the vesiculm seminales and vase deferentia; but, according to Peschier, their analysis differs slightly from prostatic concretions. Thus he found in 100 parts Phosphate of lime . 90.0 Carbonate of lime . 2.0 Animal matter . . 1.0"# Comparative Anatomy. — Assuming the prostate to be represented by a glandular structure placed at or near the termination of the vas deferens, it is found in many of the invertebrate. animals. As a general rule, it is only discovered in those pos sessed of an intrornittent organ ; this, how ever is not invariable. In the medicinal leech, among the annellata, according to Owen and Brandt, the two vase deferentia and the two sacculated vesiculx seminales send their ducts to a common prostatic body, from which the penis is continued. " In the centipede, among myriapoda, a minute efferent tube is continued from both ends of each testis, which tubes unite with those of the adjoining organ, and ultimately form a single vas deferens, which, having received the ducts of three pairs of small prostatic glands, terminate in the cloaca. ln the male aphis there is a long pyri form vesicular gland attached to each lateral vas deferens, and in many insects representa tives of prostatic glands communicate with the ductus ejaculatorius." + In the slug, among gasteropoda, the vas deferens is joined by the short and simple duct of a small pros tatic sac ; and this is the case in the common snail, in whom the duct is, however, longer. In the cephalopoda, as in the octopus, " the anterior extremity of the contractile vesicula, into which the efferent duct opens, communi cates with a wide, bent, ccecal tube (prostate), with thick glandular parietes, and having the form of a simple pouch in the sepia. The prostate in the sepiola communicates by a long and slender duct with the vesiculm semi nales." In manzmalia, two varieties of prostate are found, distinguishable as to structure from each other : one, the cellular, in which small cells open into a central cavity, from which a large duct arises ; and the other, the follicular, composed, as Miller says, " of large intesti nules, or larger ramose follicles." In the ape tribe, the form of the prostate is larger from above downwards than from before backwards, and surrounds the urethra in the form of a crescent. In position, size, and structure, it resembles that of man. In the mandril some accessory lobes are found. The prostate of the makLs sends off two pro longations, which surround the excretory ducts of the vesiculx seminales.