Under this head we comprise the morbid anatomy of the kidneys and the efferent apparatus, viz. the calices, the bladder, and the urethra; the two are of course very intimately related to one another. The abnormities of the suprarenal capsules will be considered in an appendix.

1. Defect And Excess Of Formation

The urinary apparatus is very rarely entirely deficient; it is generally found even in very imperfect monstrosities. One kidney is frequently absent, or individual portions of the system are, as we shall have occasion to see, more or less imperfectly developed.

When one kidney only is present, it is important to distinguish between the unsymmetrical and the solitary kidney. The former is represented by a right or left kidney, which is normal in regard to position and conformation, and occasionally rather enlarged, its fellow being deficient. The solitary kidney is the result of a fusion of the two organs, and therefore offers the characters peculiar to this arrangement in a greater or less degree. The lowest degree of fusion is seen in the horseshoe kidney (ren unguliformis); the two kidneys are united at their inferior portions by a flat, riband-like, or rounded bridge of tissue, which crosses the vertebral column. In the higher degrees the two lateral portions approach one another more and more, until they reach the highest degree, in which a single disk-like kidney, lying in the median line and provided with a double or a single calyx, represents complete fusion. The more intimate this union is, the more the hilus of the kidneys is directed forwards, so that whereas, in the lowest degree, it is indicated by an evidently increased development of the posterior labium of the hilus, the hilus of the solitary kidney occupies the anterior surface. The more considerable the fusion is, the more the kidneys descend along the vertebral column, and the solitary kidney is commonly situated at the promontory, or even at the concavity of the sacrum. In exceptional cases only the solitary kidney is placed, like the unsymmetrical kidney, at the side of the vertebral column, on one side of the median line.

Excess of development occurs very rarely, except in the case of biven-tral monsters, in the shape of a third kidney, situated in the median line, and generally placed at the promontory; or in the shape of a single symmetrical kidney, which is composed of two kidneys united into one.

2. Deviations Of Size

The kidneys are found enlarged or diminished in various degrees, and under various circumstances.

1. Enlargement is observed -

Firstly

Occasionally in one kidney, after its fellow has been deprived of its functions; this is a case of hypertrophy which may be considered as analogous to the increase of size in the unsymmetrical kidney;

Secondly

As congestive turgor;

Thirdly

As inflammatory swelling;

Fourthly

As a consequence of infiltration of the renal tissue induced by or independent of inflammation: various forms of Bright's disease belong to this subdivision;

Fifthly

As arising from morbid growths, in which case the enlargement corresponds to their number and size;

Sixthly

As originating in dilatation of the pelvis and calices of the kidneys; the greater in this case the increase of size, the more will the renal substance become atrophied in consequence of pressure from within. Rayer states the left kidney to be normally of greater weight and larger dimensions than the one on the right side.

Abnormal smallness is either congenital, or the result of atrophy. Spontaneous and primary atrophy occurring independent of contraction, or complete occlusion of the artery, is very unusual, and belongs almost exclusively to old age; secondary atrophy, resulting from and complicated with disease of the tissues, is much more frequent. In the case of extreme dilatation of the renal pelves and calices atrophy and enlargement appear combined.

2. Atrophy may affect the two substances of the kidney uniformly; or it may involve the cortical substance only; the latter is the more frequent case in secondary atrophy, on account of the greater proclivity to disease in the cortical substance. The tissue is rendered pale, or it may be distinguished by its darker color, and the vessels are often found varicose. We very often find an unusual amount of fat accumulated round the atrophic kidney.

We shall have occasion to enter more fully into the subject of secondary atrophy, at a future period.

3. Deviations Of Form

Besides the anomalous forms of the kidneys, resulting from fusion of the two organs, which we have already described, we may point to the lobulated kidney as an interesting conformation. It occurs as an arrest of development in the foetal state, or if acquired, as atrophy of the cortical substance, accompanied by dilatation of the calices. There are other congenital malformations of the kidneys, which are of less importance, as, for instance, the elongated kidney, which appertains to the foetal state, the round, prismatic, triangular, cylindrical kidneys, the kidneys with a transverse furrow (separation into an upper and lower half); and also various acquired malformations, which are caused by external pressure, by partial loss of substance, and atrophy.

4. Deviations Of Position

Here too we must first point to an anomaly resulting from the various degrees of fusion of the two organs, i. e. the descent of the kidneys to a lower part of the abdomen. This may, however, occur independently of the malformation alluded to, and we sometimes find one, sometimes both kidneys, as low down as the brim of the pelvis, or even as the hollow of the sacrum. The anomalies in the origin of the renal vessels which correspond to the original deviation of position deserve attention, as well as the increase in their number and the diminution of the ureter in proportion to the descent of the kidney.

The kidneys, and especially the right one, may be depressed by an enlarged liver, and the consequence is, that the hilus of the former is turned upwards, as the upper portion of the kidney is necessarily most depressed.

"We have lastly to allude to the occasional movability of the kidneys, which is owing to insufficient fixation by means of the adipose fascia, and apparently also to an elongation of the vessels; we sometimes find that the kidneys may be moved from one to two inches along the spinal column.

5. Deviations Of Consistency

The kidneys sometimes offer a diminution of consistency, or relaxation, or an increase of resistancy or toughness, without any apparent change of texture. The former occurs concurrently with a similar condition in other parenchymatous organs, and is the result of cachexia, anaemia, and marasmus, and of defibrination of the blood, from excessive exudations; the organs, in this case, are very pale and friable. Both an increase and a diminution of consistency are much more frequent as complications of textural alterations, and we shall examine them more in detail under this head. Genuine softening of the entire kidney, or of a portion of the organ, in the shape of spots of various sizes, of a dirty brown, chocolate-colored, rusty pulp, is a very rare occurrence.

6. Solution Of Continuity

This is produced not only by cutting- in-truments, but may occur in the shape of rupture, from concussion, or in consequence of falls or blows, received in the region of the kidneys. After a fall from a considerable height, rupture of the kidneys is very frequently complicated with laceration of other abdominal viscera. It gives rise to hemorrhage, inflammation, and suppuration; the latter terminates in the manner that we shall have occasion to delineate when speaking of renal abscess. Concurrent injury of the calices and of the pelvis of the kidney, causes extravasation of urine into and beyond the adipose covering of the kidneys: if the peritoneum has also suffered, a fatal termination ensues rapidly; if not, a permanent or temporary cure, with a residuary fistula, may follow.