a solution of cane sugar, mannite, or the sugar of milk, the whole of it will be found in the urine; but if we inject glucose or grape sugar, except in large quantity, none of it can be detected in that fluid. But if an animal be fed on the first mentioned varieties of sugar, they are not found in the urine; because, according to M. Magendie, digestion has transformed them into glucose, and this has become decomposed in the lungs. The following table is given by him to exhibit the quantity of the different kinds of sugar that must be injected into the jugular vein, in order that they may be detected in the urine. It shows-as he has remarked-that "the natural sugar of the economy is, destroyed in the act of respiration with far greater facility than that proceeding from alimentary substances:

These experiments are curious, and demand careful repetition. The results it has been seen-are admitted by M. Magendie; but so much evil has flowed from the too hasty reception of the phenomena presented by experiments on living animals, that the author waits for further developements.

If the excretion of the bile be prevented from any cause, we know that derangement of health is induced; but it is probable, that its agency in the production of disease is much overrated; and that, as M. Broussais has suggested, the source of many of the affections termed bilious is in the mucous membrane lining the stomach and intestines; which, owing to the heterogeneous matters constantly brought into contact with it, must be peculiarly liable to be morbidly affected. When irritation exists there, we can understand how the secretion from the liver may be consecutively modified, the excitement spreading directly along the biliary ducts to the secretory organ.

6. The Urinary Secretion.

This is the most extensive secretion accomplished by any of the glandular structures of the body, and is essentially depuratory; its suppression giving rise to formidable evils. The apparatus consists of the kidneys, which secrete the fluid; the ureters, which convey the urine to the bladder; the bladder itself, which serves as a reservoir for the urine; and the urethra, which conveys the urine externally. These require a distinct consideration.

The kidneys are two glands situate in the abdomen; one on each side of the spine, in the posterior part of the lumbar region. They are without the cavity of the peritoneum, which covers them at the anterior part only; and are situate in the midst of a considerable mass of adipous areolar tissue. The right kidney is nearly an inch lower than the left, owing to the presence of the thick posterior margin of the right lobe of the liver. Occasionally, there is but one kidney; at other times, three have been met with. They have the form of the haricot or kidney-bean, which has indeed, been called

after them; and are situate vertically, the fissure being turned inwards. If we compare them with the liver, their size is by no means in proportion to the extensive secretion effected by them. Their united weight does not amount to more than six or eight ounces. Of 65 male kidneys, weighed by Dr. John Reid,' the average was found to be 5 oz. 7 dr. for the right kidney; 5 oz. 11 dr. for the left. Of 28 female kidneys, the right weighed 4 oz. 13 dr.; the left, 5 oz. 2 dr. The left kidney generally weighs more than the right at all ages. The kidneys of the new-born child, although absolutely much lighter than those of the adult, are yet, according to M. Huschke, in proportion to the whole body much heavier; inasmuch as their weight is to that of the

Plan of a Longitudinal Section of the Kidney and Upper Part of the Ureter, through the Hilus, copied from an enlarged model.

a, a, a. The cortical substance. b, b. Broad part of two of the pyramids of Malpighi. e, e. Section of the narrow part or apex of two of these pyramids, lying within the divisions of the ureter marked c, c. d, d. Summits of the pyramids, called papillæ, projecting into and surrounded by the divisions of the ureter. c, c. Divisions of the ureter, called the calices or infundibula, laid open. e. A calix or infundibulum unopened. p. Enlarged upper end of ureter, named the pelvis of the kidney. s. Central cavity or sinus of the kidney.

whole body of the infant, as 1 to 82-100; in the adult as 1 to 225. They, therefore, do not grow uniformly with the body, although the secretion of urine becomes more energetic after birth.

The kidneys are hard, solid bodies, of a brown colour. The sanguiferous vessels, which convey and return the blood to them, as well as the excretory duct, communicate with them at the fissure.

The anatomical constituents of these organs are;-1. The renal artery, which arises from the abdominal aorta at a right angle, and,

1 Lond. and Edinb. Monthly Journal of Med. Sciences, April, 1843, p. 323.
2 Encyclop. Anatom., traduit par Jourdan, v. 321, Paris, 1845.

after a short course, enters the kidney, ramifying in its substance. 2. The excretory ducts, which arise from every part of the tissue, in which the ramifications of the renal artery terminate. They end in the pelvis of the kidney. (Fig. 351.) 3. The renal veins, which receive the superfluous blood, after the urine has been separated from it, and terminate in the renal or emulgent vein, which issues at the fissure, and opens into the abdominal vena cava. 4. Lymphatic vessels, arranged in two planes -a superficial and a deap-seated, which terminate in the lumbar glands. 5. Nerves, which proceed from the semilunar ganglion, solar plexus, &c., and surround the renal artery as with a network, following it in all its ramifications. 6. Areolar membrane, which, as in every other organ, binds the parts together. These anatomical elements, by their union, constitute the organ as we find it.

Fig. 352.

When the kidney is divided longitudinally, it is seen to consist of two substances, which differ in their situation, colour, consistence, and texture. One of these, and the more external, is called the cortical glandular or vascular substance. It forms the whole circumference of the kidney; is about two lines in thickness; of less consistence than the other; of a pale red colour; and receives almost entirely the ramifications of the renal artery. The other and innermost is the tubular, medullary, uriniferous, conoidal or radiated substance. It is more dense than the other; less red; and seems to be formed of numerous minute tubes, which unite in conical bundles of unequal size-pyramids of Malpighi-the base of which is turned towards the cortical portion, -the apices forming the papillæ or mammillary processes, and facing the pelvis of the kidney. The papillæ vary in number from five to eighteen; are of a florid colour; and upon their points or apices are terminations of uriniferous tubes large enough to be distinguished by the naked eye. Around the root of each papilla, a membranous tube arises called calix or infundibulum: this receives the urine from the papilla, and conveys it into the pelvis of the kidney, which may be regarded as the commencement of the ureter. The cortical part of the kidney is the most vascular; and the plexus formed by the tubuli uriniferi appears to come there in closest relation with that formed by the renal capillaries. In the illustration (Fig. 352) of the two portions as they appear in the new-born infant, A exhibits them of the natural size:-1, 1, Corpora Malpighiana or Malpighian bodies, appearing as points in the cortical substance. 2. One of the papillæ. These Malpighian bodies are scattered through the plexus formed by the blood vessels and uriniferous tubes. Each one, when examined by a high magnifying power, is found to consist of a convoluted mass of minute bloodvessels. In them-it was at one time supposed-the uriniferous tubes originate; but the examinations of Müller and Huschke have seemed to show, that they are only capable of injection from

Portion of Kidney of
New-born Infant.

A. Natural size. B. magnified. 1, 1. Cor

A small portion of A pora Malpighiana. 2.

Tubuli uriniferi.

(Wagner.)

Small Portion of Kidney magnified 60 diameters.

Bifurcated tubuli. 4, 5, 6. Tubuli converging towards the papilla. 1. Cacal extremity of a tubulus. 2, 2. Loops of tubuli. 3, 3.

7, 7, 7. Corpora Malpighiana. 8. Arterial trunk.

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the arteries or veins. They are found in the kidneys of most, if not all, of the vertebrata. In the cortical substance, according to Wagner, the tubuli can be traced, although with difficulty, winding among the vascular plexuses or skeins, mostly looped towards the margin of the organ, and running into one another, or having blind or cæcal extremities; more rarely enlarged and club-shaped as in Fig. 48, and occasionally cleft (Fig. 353). The entire cortical substance, according to Wagner, consists of convolutions of the uriniferous tubes, which present a nearly uniform diameter, on an average, from about the 60th to the 50th of a line. Professor Goodsir, however, without denying the existence of occasional blind extremities of the tubuli uriniferi- the result probably, he thinks, of arrested developement -states, that he has never seen the ducts terminate in this way. He has described a fibro-cellular framework, which, pervading and particularly its corevery part of the gland, tical portion, performs

2

the same office in the kidney, which the capsule of Glisson does in the

1 Elements of Physiology, by R. Willis, § 193, Lond., 1842.

2 Lond. and Edinb. Monthly Journ. of Med. Science, May, 1842.

liver,-being a basis of support to the delicate structure of the gland, conducting the blood vessels through the organ, and constituting small chambers in the cortical portion, in each of which a single ultimate coil or loop of the uriniferous ducts is lodged. Mr. Goodsir believes, that the urine is formed at first within the epithelium cells of the ducts, and that these burst, dissolve, and throw out their contents, and are succeeded by others, which perform the same functions. The urine of man has not been detected by Mr. Goodsir within the cells, that line the ducts, but he has submitted to the Royal Society of Edinburgh a memoir, already referred to, in which he has endeavoured to show,

Tubuli Uriniferi. (Baly.)

A. Portion of a secreting canal from the cortical substance of the kidney. B. The epitheJium or gland-cells, more highly magnified (700 times). c. Portion of a canal from the medullary substance of the kidney. At one part the basement membrane has no epithelium liningit.

Plan of the Renal Circulation. (Bowman.)

a. A branch of the renal artery giving off several Malpighian twigs. 1. An afferent twig to the capillary tuft contained in the Malpighian body, m; from the Malpighian body the uriniferous tube is seen taking its tortuous course to t. 2, 2. Efferent veins: that which proceeds from the Malpighian body is seen to be smaller than the corresponding artery. p, p. The capillary venous plexus, ramifying upon the uriniferous tube. This plexus receives its blood from the efferent veins, 2, 2, and transmits it to the branch of the renal vein, v.

that urine, bile, and milk, as well as the other more important secretions in the lower animals, are formed within the nucleated cells of the ducts themselves; and he is of opinion, that the urine of man is poured at first into the cavities of the nucleated cells of the human kidney.

Mr. Bowman' has affirmed, that the kidney is furnished with a true portal system, and that the urine, like the bile, is secreted-in part at least-from blood, traversing at the time a second set of capillaries. According to him, each of the exceedingly tortuous and convoluted urinary conduits terminates, at its final extremity, by a contracted neck, which leads into a little chamber or cyst,-capsule of Malpighi -in which is contained the true glandule, corpuscle or glomerule of Malpighi. This consists of a tuft or coil of capillary blood vessels, totally naked, which originates in one of the ultimate branches of the

1 Proceedings of the Royal Society, No. lii., Feb. 3, 1842; and Philos. Transactions, Pt. 1, p. 57, Lond., 1842.