acid is increased, and sometimes diminished. The sulphates, phosphates, and chlorides are generally increased.

The general result of experimental observations on the effects of exercise upon the urine may be summed up in the proposition that this condition increases the activity of the nutritive processes, and produces a corresponding activity in the function of disassimilation, as indicated by the amount of excrementitious matters separated by the kidneys.'

Influence of Mental Exertion.-Although the influence of mental exertion upon the composition of the urine has not been very much studied, the results of the investigations which have been made upon this subject are, in many regards, quite satisfactory. It is a matter of common remark that the secretion of urine is very often modified to a very great extent through the nervous system. Fear, anger, and various violent emotions sometimes produce a sudden and copious secretion of urine containing a large amount of water, and this phenomenon is very often observed in cases of hysteria. Very intense mental exertion will occasionally produce the same result. We have often observed a frequent desire to urinate during a few hours of intense and unremitting mental labor; and on one occasion, being struck with the amount of urine voided, it was found, on examination, to present scarcely any acidity and a specific gravity of about 1002. The interesting point in this connection, however, is to observe the influence of mental labor upon

1 Dr. J. C. Draper made, in 1856, a number of observations upon the effect of exercise on the excretion of urea, from which he concluded that rest does not diminish this excretion, and that exercise does not increase, but actually lessens, the quantity discharged. These conclusions are arrived at by comparing the amount of urea excreted by a patient confined to the bed with a fractured leg, with the average of eighteen observations upon other persons. The necessary experimental conditions are no better fulfilled in the other observations than in this, and the conclusions arrived at cannot therefore be accepted, in opposition to the accurate experiments of other observers (DRAPER, Is Muscular Motion the Cause of the Production of Urea?—New York Journal of Medicine, 1856, New Series, vol. xvi., p. 155, et seq.).

the elimination of solid matters, as contrasted with the amount of excretion during complete repose, the conditions of alimentation in the two instances being identical.

The most extended series of observations upon this subject, in which all the necessary experimental conditions were fulfilled, are those of Prof. Hammond. These experiments commenced with a standard series of observations, under fixed conditions of diet, exercise, etc., extending over a period of ten days. With a view, then, of determining the influence of increased mental exertion, the number of hours in the day appropriated to study was doubled, the conditions of food and exercise remaining the same as in the standard series. The average of a series of observations, extending over ten days, showed an increase in the quantity of the urine, and an increase, also, in the quantity of all of its solid constituents, with the exception of uric acid, the proportion of which was notably diminished. The amount of variation was as follows:

Average of ten days in the standard series: Quantity of urine, 37.95 oz.; urea, 671-32 grains; uric acid, 14:44 grains; chlorine, 154-29 grains; phosphoric acid, 43-66 grains; and sulphuric acid, 38:47 grains.

Average of ten days with increased mental exertion: Quantity of urine, 43·56 oz.; urea, 749-33 grains; uric acid, 10.75 grains; chlorine, 172-62 grains; phosphoric acid, 66·15 grains; sulphuric acid, 49.05 grains.

In another series of experiments, also extending over ten days, in which there was absence, as far as practicable, of mental exertion, the quantity of urine was diminished, and there was a decrease in the proportion of all of its solid constituents.'

These interesting observations have since been confirmed by a number of different series of experiments; and in a

1 HAMMOND, Urological Contributions.—American Journal of the Medical Sciences, Philadelphia, 1856, New Series, vol. xxxi., p. 330, et seq., and Physiological Memoirs, Philadelphia, 1863, p. 17, et seq.

THUDICHUM, A Treatise on the Pathology of the Urine, London, 1858, pp. 163, 164.

very interesting work upon the influence of cerebral activity upon the composition of the urine, by Byasson, they have been somewhat extended. Byasson found that by mental exertion the quantity of urine was increased; the amount of urea was also increased; the phosphoric acid was increased about one-third; the sulphuric acid was more than doubled; and the chlorine was nearly doubled.'

These facts have an important bearing upon our knowledge of the effects of mental exertion upon the process of disassimilation of the nervous tissue. They show that nearly all of the solid principles contained in the urine are increased in quantity by prolonged intellectual exertion, but they fail to point to any one excrementitious principle, either organic or inorganic, which is specially connected with the physiological wear of the brain. It has been assumed that elimination of the phosphates, increased out of proportion to the increase of the other solid matters of the urine, is one of the constant effects of intellectual effort; but this view is not sustained by direct physiological experiments, nor by facts in pathology. We have already discussed this question somewhat elaborately, under the head of the phosphates of the urine."

1 BYASSON, Essai sur la relation qui existe à l'état physiologique entre l'activité cérébrale et la composition des urines, Paris, 1868, p. 48, Table.

See p. 215.

CHAPTER VIII.

PHYSIOLOGICAL ANATOMY OF THE LIVER.

Coverings and ligaments of the liver-Capsule of Glisson-Lobules-Branches of the portal vein, the hepatic artery and duct—Interlobular vessels-Lobular vessels—Origin and course of the hepatic veins—Interlobular veins— Structure of a lobule of the liver-Hepatic cells-Arrangement of the bile-ducts in the lobules-Anatomy of the excretory biliary passages— Vasa aberrantia-Gall-bladder-Hepatic, cystic, and common ductsNerves and lymphatics of the liver-Mechanism of the secretion and discharge of bile-Secretion of bile from venous or arterial blood-Quantity of bile-Variations in the flow of the bile-Influence of the nervous system on the secretion of bile-Discharge of bile from the gall-bladder.

THE liver, by far the largest gland in the body, is now known to have several entirely distinct functions; and one of the most important of these has already been fully considered, in connection with digestion.' It is true that we know very little with regard to the exact office of the bile in digestion, but that this function is essential to life, there can be no doubt. We have, however, more positive information with regard to the excrementitious function of the liver and the changes which the blood undergoes in passing through its substance; and the study of these functions is closely connected with the anatomy of the liver and the chemical constitution of the bile.

Physiological Anatomy of the Liver.

It is unnecessary, in this connection, to dwell upon the ordinary descriptive anatomy of the liver. It is sufficient 1 See vol. ii., Digestion, p. 360, et seq.

to state that it is situated just below the diaphragm, in the right hypochondriac region, and is the largest gland in the body, weighing, when moderately filled with blood, about four and a half pounds. Its weight is somewhat variable, but it is stated by Sappey that in a person of ordinary adipose development, its proportion to the weight of the body is about one to thirty.' In early life, the liver is relatively larger, its proportion to the weight of the body, in the newborn child, being as one to eighteen or twenty."

The liver is covered externally by peritoneum, folds or duplicatures of this membrane being formed as it passes from the surface of the liver to the adjacent parts. These constitute four of the so-called ligaments that hold the liver in place. The proper coat of the liver is a very thin, but dense and resisting fibrous membrane, adherent to the substance of the organ, but detached without much difficulty, and very closely united to the peritoneum. This membrane is of variable thickness at different parts of the liver, being especially thin in the groove for the vena cava. At the transverse fissure it surrounds the duct, blood-vessels, and nerves, and penetrates the substance of the organ in the form of a vagina, or sheath, surrounding the vessels and branching with them. This membrane, as it ramifies in the substance of the liver, is called the capsule of Glisson. It will be more fully described in connection with the arrangement of the hepatic vessels.

The substance of the liver is made up of innumerable lobules, of an irregularly ovid or rounded form, and about

of an inch in diameter. The space which separates these

1 SAPPEY, Traité d'anatomie descriptive, Paris, 1857, tome ii., p. 261. Sappey made a number of examinations of the weight of the normal liver, with the vessels moderately distended with water, in order to represent, in a measure, its physiological condition. He estimated the weight from the average of ten livers, taken from both sexes and at different ages after adult life, at two kil., or about four and a half pounds. The weight of the liver with the vessels empty is about three and one-third pounds.

WILSON, Cyclopædia of Anatomy and Physiology, London, 1839-47, vol. iii., p. 178, Article, Liver.