Vesical calculi are usually ovoid in form, with their surfaces sometimes slightly and unequally flattened. If they have been enclosed, or partly enclosed, in a pouch or offshoot from the bladder, they may be round, oblong, irregular, or dumb-bell shaped. The majority are of a dark-brown hue; some are palish - gray, others yellowish - brown, and a few whitish-gray. All, with rare exceptions, present a rough asperous surface (fig. 162), usually more marked on one side than the other. The side on which the stone rests while in the bladder is smoother, denser, and less rounded than the other surface. In some the asperities are coarse and rounded, and impart to the stone a distinct mulberry character, but in the majority they are finer, closer set, and less prominent. In density calculi vary very considerably in different specimens, and also in different parts of the same specimen, but it is rare to find them of that flinty hardness which characterizes some examples of vesicular calculus in man. In many instances they present an open spongy texture and are distinguished by marked brittleness and want of cohesion. As a rule the inner portion of the stone is the more hard and compact, while the outer portion is less consistent, and, in some instances, so soft as to be readily broken down with the fingers into small rounded or angular fragments. To examine the structure of these formations the stone should be first cut with a saw and the divided surface rubbed even and smooth on a wet stone.

Vesical Calculus.

Fig, 162. - Vesical Calculus.

If the polished face be now examined it will be seen to present certain structural markings, of which the following are the more common examples: -

1. A regular series of closely-arranged concentric rings (fig. 163), representing sections of a succession of layers of earthy matter. Of these some are narrow, some broad, some yellow or pale brown, and we gather, by the use of the knife, that they are soft or hard according as they have been quickly or slowly deposited. In this variety the stone, as a whole, is usually hard and its texture compact.

2. The laminae are irregular and incomplete, sometimes interrupted by small sinuous cavities or irregular spaces containing free earthy granules and epithelial debris.

3. Sectional surface irregular, and marked by sinuous fissures (fig. 164). Centre excavated and enclosed by a narrow strong band, from which arborescent rays proceed to the circumference and terminate in asperities on the surface, giving to the section a rough, coarse appearance.

Section of Vesical Calculus.

Fig. 163. - Section of Vesical Calculus.

Section of Vesical Calculus.

Fig. 164. - Section of Vesical Calculus.

Section of Vesical Calculus.

Fig. 165. - Section of Vesical Calculus.

4. Small groups of concentric rings forming rounded, solid - looking bodies varying from the size of a hemp-seed to that of a bean (fig. 165). They are separated from each other by a structureless mass of earthy matter, usually of less density than themselves, and in which fissures and cavities are sometimes met with. This variety consists of a number of small laminated calculi, aggregated together and enclosed in an amorphous deposit.

CALCULI. Cystic Calculus having a piece of stick as a nucleus. Bladder of Horse.

PLATE XXX. CALCULI. Cystic Calculus having a piece of stick as a nucleus. Bladder of Horse.

CALCULI. Renal Calculus. Kidney of Horse.

PLATE XXX. CALCULI. Renal Calculus. Kidney of Horse.

All vesical calculi do not originate in the bladder. Some no doubt have their beginning in the pelvis of the kidney, in which position we have repeatedly found them in their rudimentary condition. Many of these renal formations, on reaching the bladder, are ejected with the urine, but occasionally such as acquire large dimensions are retained in the vesical cavity and undergo enlargement by earthy incrustation.

It is certain, however, that stone formation is not always the direct outcome of the conditions indicated above. Foreign substances, we are aware, sometimes find their way into the bladder of the horse, notwithstanding the seeming difficulty of such an event. Some years ago Mr. William Hunting, of London, brought to the notice of the Central Veterinary Medical Society such a case, where a piece of stick, some four or five inches in length, and as thick as the little finger, was found stretching across the bladder of a horse, with one end projecting through its walls into the pelvic cavity. It had evidently occupied this position some considerable time, as a large calculus had formed around its central portion. Whence the stick had come there was no direct evidence to show, and we are left to assume its possible introduction through the abdominal walls or through the alimentary canal. Such an accident as that first referred to is quite possible, but for many considerations does not recommend itself to our acceptance. From facts which have recently come to light in the human subject, we are more disposed to accept the explanation which refers its entrance into the bladder through the medium of the alimentary canal.