thesis which gives a perfectly satisfactory explanation of all the physiological and chemical processes of urinary secretion. We must therefore look upon the excretion of urine as a compound process of secretion and filtration.

[The theory of secretion, pure and simple, has perhaps gained ground recently owing to the advocacy of Heidenhain* and his followers. He accepts the facts, abundantly proved by Nussbaum and others, that the specific constituents of the urine, such as urea, are secreted by the epithelium of the urinary tubules, and that the water and salts come from the glomeruli, not by mere filtration, but by specific action of the cells covering the glomerular tufts. These cells, moreover, when in normal condition, prevent the passage of albumen, and only allow it to escape in case of lesion or deficient nutrition. Senator,† in our opinion, has, however, ably controverted this view as applied to the glomeruli, and the separation of urine is to be considered now, as when the first edition of this work was presented, as a combination of both filtration and secretion.]

[*Hermann's "Handbuch der Physiologie," Bd. V., Part i.

+ "Albuminuria in Health and Disease," and Appendix (1), by Dr. H. Senator. "New Sydenham Society Publications," 1884.]

CHAPTER III.

THE URINE.

A. A GENERAL DESCRIPTION.

THE urine is the secretion of the kidneys, and under normal conditions is essentially a solution of such ingredients as belong to retrograde tissue-metamorphosis. It is a solution of urea and chloride of sodium, to which are added in less proportion other organic and inorganic constituents of the blood, as well as certain foreign matters introduced into the organism, which are excreted through the kidneys unaltered or having previously undergone chemical transformation.

In a normal condition the urine contains in part organic constituents, as urea, uric acid, creatinine, hippuric acid, xanthine, lactic acid, coloring matters, indican, grape sugar (Brücke), [albumen (Senator)], etc.; partly inorganic, as chloride of sodium, phosphates of sodi um, magnesium, and calcium, sulphates of the alkalies, ammonium salts, iron (as a constituent of the coloring matters), and gases-carbonic acid, nitrogen, and oxygen. In pathological urine, besides the normal constituents, are found also albumen, grape sugar, inosite,

biliary matters, fat, sulphuretted hydrogen, coloring matters of the blood, uroerythrine (Heller), leucine, and tyrosine, oxalate and carbonate of calcium, carbonate of ammonium, cystine, pus, blood, epithelium, spermatozoa, fungi, and infusoria.

Before we take into consideration the semeiotic significance of the urine, we will describe its peculiarities as far as important to our subject, and the most useful methods of investigation.

B. PHYSICAL CHARACTERISTICS.

1. Amount.

The amount of urine excreted by a healthy person, who eats and drinks moderately, varies between 1,400 and 1,600 c.c., the mean average for the twenty-four hours being 1,500 c.c.

One passes most in the afternoon, less in the morning, and the least at night; for, under ordinary conditions, in regard to its quantity, the morning urine is least influenced by meals and other circumstances, and approaches a mean between the excretions of afternoon and night. The urine increases in proportion to the amount of imbibed fluids (urina potus). Its amount is increased also, though much less perceptibly, by cold and atmospheric moisture, whereby the perspiration is lessened. During rest, or by such circumstances as profuse perspiration or profuse diarrhoea, the urine diminishes.

2. Specific Gravity.

The specific gravity of normal urine (1,500 c.c.) is between 1.015 and 1.021. When the amount of urine is lessened, the specific gravity is correspondingly increased, standing in inverse ratio. Pathologically the urine varies between 1.003 and 1.040. Especially important are those cases in which we find with a lessened volume a lower, and with a greater volume a higher, specific gravity. We often find a higher specific gravity in mellituria, in the beginning of acute febrile diseases, and after the administration of neutral salts. An increased amount and a specific gravity between 1·030 and 1040 is suggestive of mellituria. A lower specific gravity is to be observed in hydruria, urina spastica, and urina potus.

The specific gravity is best obtained by means of a pyknometer, or by scales; though for practical purposes less complicated means of investigation answer. For immediate determination the urinometer is very convenient.

The surest method of ascertaining the exact specific gravity by the urinometer is as follows: One fills a small standing glass cylinder tube four fifths full of the urine; the froth being removed by filter paper, the urinometer is allowed to sink into the urine guided by the supported right hand, never being allowed to come into contact with the side of the tube. Bring the eye on a level with the surface of the urine, and read the division corresponding with this surface (not the upper

rim of the fluid raised slightly on the stem by attrac tion). Touch the stem, causing the urinometer to sink slightly in the fluid; and, when it comes to rest, read again.

In all urinometrical observations, the urine should have a temperature between 12° and 17° C.; otherwise considerable errors may be made.

If the amount of urine is small, dilute with even three or four volumes of water: test as directed above, and multiply the number read off by the number of volumes made by the dilution. For example: If three volumes of water be added to one volume of urine, and we read 1.008, to obtain the real specific gravity of the original fluid 1.008 is multiplied by 1+3=4 (1·008 X 4 1.032). The solid materials (on which the specific gravity depends) which formerly were dissolved in one volume are after the dilution dissolved in four volumes: the specific gravity is therefore only one fourth of the specific gravity of the original; or, what is the same thing, the specific gravity of the original is four times the specific gravity of the dilution.

3. Solid Ingredients.

In normal urine the solid materials excreted in twenty-four hours are generally 60 to 70 grammes. Should we find say 200 grms., diabetes is indicated. If, on the contrary, we find a very small amount of solids excreted, say 20 grms., and the quantity of urine not correspondingly diminished, it indicates hydruria. In