Opposed to these renal stimulants are renal sedatives or depressants, which appear to diminish directly the activity of the renal cells, when they reach them through the blood. Morphia has this effect, and possibly quinia (p) and other substances.

III. Pathological Relations

The disorders of the renal functions, which will be taken by 2 h-8 us to illustrate the application of the measures just noticed, may be summarised as follows:

1. Disorders Of The Fluid Secretion Referable To The General Blood Pressure

Disorders Of The Fluid Secretion Referable To The General Blood Pressure. (a) Diminution of the general arterial pressure, which is generally referable to heart disease, leads to marked disturbance of the urinary flow. We saw under the head of the circulation (page 472) how dilatation of the heart lowers the pressure in the arteries and raises it in the veins, i.e. lowers it in the afferent vessel of the glomerulus, and raises it in the efferent vessel, thus causing congestion of the kidneys. The urine in this class of cases contains albumen and blood proceeding from the engorged veins; it falls in quantity in consequence of the fall in the arterial pressure, and of obstruction in the tubules, which become choked with fibrinous casts; and the total excretion of solids is diminished, as the result of retardation of the blood current.

(b) Increase of the general arterial pressure is associated with that form of chronic disease of the kidney known as the"Granular or Contracted Kidney." Here the urine is very abundant, probably reaching several times its normal volume, very light in colour and weight, and may contain a trace of albumen. The tension of the radial artery is high; the left ventricle is hypertrophied; and the patient often dies of secondary dilatation of the heart, or of rupture of an artery in the brain. As far as the kidney is concerned, the condition is one of constant pathological diuresis.

2. Disorders Of The Fluid Secretion, Referable To The Local Blood Pressure

Disorders Of The Fluid Secretion, Referable To The Local Blood Pressure. (a) Certain nervous conditions disturb the pressure in the kidney by causing contraction or dilatation of the renal vessels, and thus modifying the amount of urinary water. Such a condition may be either central or local, direct or reflex. Thus hysteria is attended by alternately profuse and deficient flow of urine. Disease of the medulla and its neighbourhood may give rise to profuse diuresis (diabetes insipidus), which has been traced in other cases to disease of the renal nerves. Reflexly, the chief cause of disturbance of the renal secretion is injury or disease of the prostate or urethra, which may even lead to fastal suppression.

b. Morbid conditions of the blood-vessels of the kidney, such as disease of the glomeruli, arteries and veins, which constitute one of the elements of Bright's disease, produce a variety of dis-tuibances in the volume and constitution of the urine, according to their exact seat and degree. Pressure on the trunks of the renal vessels by abdominal enlargements may also cause serious disturbance of the renal circulation, with albuminuria, haemorrhage, or even suppression of urine as the result.

3. Disease Of The Secreting Epithelium

Disease Of The Secreting Epithelium. This constitutes another element of Bright's disease. The diseased cells fail in function, choke up the tubules, press upon the venous plexus, and thus give rise at once to stagnation of the blood current and resistance to the filtration of water through the glomerulus. The clinical phenomena of this condition (commonly called the Large White Kidney), are very definite. The urine falls in volume; the solids are absolutely diminished, but relatively increased, so that the specific gravity is high; and in their place there appear albumen, probably derived directly from the venous plexus, blood from the same source or from the glomeruli, and casts formed of diseased cells, fibrin, etc. The blood becomes poisoned by retention of urea. The systemic vessels become diseased, and the heart hypertrophied; and the blood-change and cardiovascular disease together lead to marked breathlessness, and to escape of the watery parts of the blood into the tissues and serous cavities, constituting renal dropsy.

4. Rise of pressure within the uriniferous tubules is a serious cause of complete arrest of the secretion. This is one of the effects of fulness of the venous plexus, and of epithelial accumulations in the tubes, already noticed; and may also originate in obstruction of the ureter, disease or injury of the bladder and prostate, or stricture of the urethra.

5. The Condition Of The Blood

The Condition Of The Blood. This is the most common of all the causes of derangement of the urinary secretion. A number of the disorders of the urine, as regards its reaction and relative composition, can be traced to dyspepsia, hepatic derangement, and defective oxygenation or metabolism; and even albumen, sugar, and bile may find their way into the urine from the same causes. One striking disorder of the urine is characterised by unnatural alkalinity and by its effects in precipitating the solid constituents. The urine is turbid from precipitation of phosphates, carbonates, and urates; and these are deposited in the passages, causing pain and irritation. If the natural acidity of the urine between meals be insufficient to dissolve these alkaline deposits, concretions are formed, and grow at each period of indigestion, until they form a calculus, which may travel downwards and be expelled with the urine after great suffering.

A similar disorder of. the urine is characterised by excessive acidity. This has different causal relations, but the ultimate effects are practically the same-the precipitation of uric acid and urates, and possibly the formation of calculus. Excessive acidity is chiefly met with in the subjects of disorder of the liver from indulgence in proteid food (see page 443); and may be accompanied by an excess of urea, diminution of water, and occasionally by traces of albumen and sugar.

IV. Natural Recovery