and form a single, narrow vessel which makes its exit from the corpuscle, in proximity to the entering artery, and is, therefore, termed the efferent vessel. This efferent vessel is arterial in character, so that the relation between it and the afferent artery is not that subsisting between arteries and veins. It is interesting to observe that the arrangement of the minute vessels, forming the malpighian tufts, is such that the finest capillaries of the coil are always found in the locality where the corpuscle opens into the tubule, or, in other words, at the point where the latter commences.

There can be no doubt that, as was first pointed out by Mr. Bowman, the special function of the malpighian tufts of capillaries placed within the corpuscles which are continuous with the tubules, is to separate the water of the urine from the blood, for which purpose they are admirably contrived. To use the words of Mr. Bowman: A large artery breaks up in a very direct manner into a number of minute branches (afferent vessels), each of which suddenly opens into an assemblage of vessels of far greater aggregate capacity than itself, and from which there is but one exit. Hence must arise a

1 Todd and Bowman's Physiological Anatomy and Physiology of Man, vol. ii. p. 495.

very abrupt retardation of the current of blood. The vessels in which this delay occurs are uncovered by any structure. They lie bare in a cell, from which there is but one outlet.' The effect of the impediment to the flow of blood, by the mechanism thus described, through the coils of capillaries, is to produce a considerable lateral pressure on their walls, which pressure must cause the continuous escape of a considerable quantity of the water of the blood serum through the opposing membrane. But, as in the normal condition albumen does not pass out with the water, it is evident that these capillary walls must possess some structural condition or peculiarity, at present unexplained, which secures the retention of the one, and permits the escape of the other. Probably the retention of albumen is due to its colloidal character. But certain disturbing influences, or morbid conditions, increase the lateral pressure of the blood on the walls of the malpighian capillaries beyond a normal degree, and thus produce such an amount of distention that albumen escapes, and is found in the urine; in other words, blood serum escapes instead of water, and a little saline matter.

Such, then, is the arrangement and office of the capillary vessels of the malpighian tufts; the

efferent vessels formed by their union (one for each tuft), after emerging from the corpuscles, break up into a fine, close, roundish angular, network of capillaries, which are everywhere distributed between the convoluted tubules, which they surround on all sides, and with which they are in contact. This network is continuous throughout the whole cortical substance of the organ. The capillaries supplying the medullary cones, which are not so vascular, are derived from the same source, but are larger and not so numerous; they follow a somewhat direct course amongst the straight tubules, and ramify only to a slight degree. In this manner is formed the proper capillary system of the kidneys; analogous to that of other glandular organs, and conveying the pabulum for the nutrition of their tissues and the materials for their proper secretion. It is needless to add, that the capillary network just described terminates in the venous radicals of the organ.

A careful study of the remarkable distribution and of the anatomical relations of the renal vessels, reveals the following peculiarities of great importance in a pathological point of view.

1. That the capillaries of the kidneys form two distinct sets: a proximate and a distal.

2. That the proximate capillaries—the malpighian

tufts-consist of a series of globular coils of short nonanastomosing vessels, each coil being placed within a dilated extremity of a uriniferous tubule, and terminating abruptly in a single narrow vessel.

3. That the distal capillaries are formed by the ramification and anastomosis of the narrow vessels in which the primary terminate, and are placed outside and between the uriniferous tubules.

4. That the whole of the blood of the renal artery must first pass through the proximate capillaries, where its flow is much impeded, before it enters the distal capillaries; and, consequently, any impediment to the circulation through the distal must immediately cause a damming back of the blood in the proximate vessels and mechanical distention of their walls.

I shall show, further on, that these peculiarities of the renal circulation have an important relation to the production of albuminuria.

The matrix or stroma of the kidney, in which the tubules and blood-vessels are embedded, and by which they are held in position, may be regarded as the skeleton or framework of the organ; it is composed of interlacing fibres of areolar tissue, and is more fully developed in the medullary than in the cortical substance; but on the surface of the latter

it becomes considerably condensed, so as to assume a membranous form, and is loosely connected with the capsule enveloping the organ.

The capsule enveloping the kidney is a smooth, whitish, thin, but firm membrane of dense fibroareolar tissue, with a network of numerous elastic fibres. The great firmness of this fibrous membrane gives it particular significance in relation to the albuminuria of Bright's disease, as I shall have occasion to point out.

Such, then, are the chief structural peculiarities of the kidneys; which require to be understood in order to investigate the different pathological conditions grouped under the designation of Bright's disease.

Pathological research and clinical observation, of late years, seem to have fully established that there are at least three distinct or typical forms of chronic renal affection included under the term Bright's disease: these being, 1, the cirrhotic kidney, 2, the waxy kidney, 3, the fatty kidney. Each form commencing in one of the three histological elements composing the organ, and ultimately destroying its normal structure. This classification of course excludes mixed cases, in which different forms are combined. I shall briefly advert to the two former of these diseased conditions, and then enter