tubules and capillaries and the capsule of the kidney, and to study carefully the manner in which this relation is disturbed by the morbid changes which have taken place in the organ.

Fatty degeneration of the kidneys is essentially a disease of the glandular epithelium of the convoluted tubules, which become swollen and distended by morbid accumulations. But the tubules are pent up in a limited space surrounded by the dense, fibrous, and remarkably firm capsule which yields very slowly and gradually to the internal pressure exerted on it by their increased bulk and solid consistence; the result being, that as room is not made for them with sufficient rapidity by the expansion of the capsule they become approximated, and press against each other so closely and firmly that the whole of the distal, or proper, capillaries of the organ, distributed everywhere between and around them, become so squeezed and compressed that there is no longer a free, healthy flow of blood through these vessels, but instead, there becomes established a permanent mechanical obstruction, more or less intense, to the onward passage of the blood out of the proximate or malpighian capillaries, and in consequence it becomes dammed back in them, and distends their walls to such a degree that a

portion of the blood serum escapes with the water of the urine, and thus albuminuria becomes permanently established. Exactly the same process takes place in dropsy from mechanical impediment to the venous circulation, as in anasarca from heart disease, or in ascites, from cirrhosis of the liver; with this difference only, that in these instances the effused serum accumulates in the areolar tissue or in a serous cavity, instead of escaping from the body.

It is necessary to add that the compressing action of the swollen tubules on the capillaries between them is favoured by the feebleness of the circulation in these vessels; its force having been broken immediately behind them by the retardation of the blood in the malpighian tufts. The capillaries of the malpighian tufts are shielded from the compression of the distended tubules, first: because they are seated within the dilated globular extremities of the tubules themselves; secondly: because they are short non-anastomosing vessels twisted and coiled into spherical masses; and thirdly: because they are next to the arteries, and are thus kept distended by the systolic force of the heart's action, which powerfully counteracts the influence of external pressure on their surfaces.

Retention of water in the blood, causing a scanty

secretion of urine, is due to the same agency as the albuminuria, namely distention of the tubules, and obstruction to the circulation through the renal capillary plexus.

It has been calculated by Brown Séquard' that in the healthy adult the quantity of blood passing through the kidneys reaches the enormous amount of 2,000 pounds per diem. Each portion of the blood loses a portion of its water in its retarded passage through the capillaries of the malpighian tufts. It is, therefore, evident that the absolute quantity of water escaping from these vessels during a definite period must be in a direct ratio to the whole amount of blood which has circulated through them. Consequently, when the quantity of this blood is greatly diminished by obstruction of the capillaries immediately in front of them, the water secreted by the kidneys daily must be proportionately reduced. It follows therefore that the degree of scantiness of the urine is a certain index of the degree of renal capillary obstruction existing in any given case.

The deficient secretion and consequent retention in the blood of the solid constituents of the urine, or uræmia, in this disease, is a fact too well established to require further illustration. It is a con

1 Journal de la Physiolog. tom. i. p. 335, 1858.

dition attributable to the combined operation of two causes, namely: the diseased state of the glandular epithelial cells of the kidneys, rendering them incapable of performing their proper function: and the greatly diminished circulation through the proper renal capillaries; it is these vessels which, in the healthy state, convey to the secreting cells of the tubules the materials for their secretion. It follows, therefore, that when these materials, the solids of the urine, are conveyed into the kidneys in quantity much reduced below the normal standard, in consequence of a greatly reduced flow of blood through these organs, they must necessarily accumulate in the blood; especially when the greater proportion of the secreting cells have lost their functional activity. This accumulation, however, is in many instances retarded by dropsical effusions and vicarious discharges from the intestines.

The morbid changes produced in the blood by the conditions just described deserve the most careful consideration; inasmuch as it is to these alterations that a fatal termination of the disease is to be ascribed in almost every instance.

The persistent drain of albumen from and the retention of water in the blood, by destroying the normal relative proportion of its ingredients,

seriously alter its physical characters, and impair its vital properties. Thus the proportion of albumen is very greatly diminished, and that of water as greatly increased; so that the specific gravity of the blood serum falls from its normal degree of 1028° or 1030° to so low, even, as 1018,° as has been ascertained by Professor Christison.1 Dr. Babington found the albumen reduced from 65 to 69, its normal proportion in healthy blood, to so low as 16 parts in 1,000. The quantity of blood corpuscles also invariably undergoes a great and rapid diminution in consequence of the hydromic and probably uræmic condition of the blood. Hence the peculiar pale, pasty, anæmic appearance suffering from Bright's disease. constituents of the blood are in many instances reduced from 100 or 102, their normal proportion, to so low as even 61 in 1000 parts; it thus loses much of its colloidal character, and its water, containing dissolved albumen and salts, transudes through the walls of the blood-vessels, the process being favoured by an impediment to the capillary circulation and vascular plethora. But, it must be observed, that the degree to which the blood suffers

presented by those In short, the solid

1 Tweedie's Library of Medicine, vol. iv. p. 282.

2 Quoted by Sir Thomas Watson, Lect. on the Pract. of Phys. vol. ii. p. 677, 4th ed.