sized cow, the smallest quantity obtained, in an experiment extending over a period of twelve hours, was 625 grammes in fifteen minutes; that is, 2500 grammes per hour, or 60 kilogrammes per day. In another experiment with a young bull weighing 185 kilogrammes, he actually withdrew from the thoracic duct in the course of twenty-four hours, 15 kilogrammes of lymph and chyle, representing a little more than 8 per cent. of the entire bodily weight of the animal.

We have obtained similar results from experiments upon the dog and goat. In a young kid weighing 6.36 kilogrammes, we have obtained from the thoracic duct 122.5 grammes of lymph in three hours and a half. This quantity represents 35 grammes per hour, and, if continued throughout the day, would amount to 640 grammes, or fully 10 per cent. of the entire bodily weight. In the dog the fluids discharged from the thoracic duct are less abundant. The average of all the results obtained by us, in this animal, at different periods after feeding, gives very nearly four and a half per cent. of the bodily weight, as the total daily quantity of lymph and chyle. This is substantially the same result as that obtained by Colin in the horse; and for a man weighing 65 kilogrammes, it would be equivalent to about 3000 grammes of lymph and chyle per day. But this quantity represents both the products of lymphatic transudation and those of intestinal absorption taken together. An estimate of the total amount of the lymph alone must be based upon the quantity of fluids passing through the thoracic duct in the intervals of digestion, when no chyle is being taken up from the alimentary canal. In the dog, as shown by the experiments quoted above, the average quantity obtained, from the thirteenth to the eighteenth or nineteenth hour after feeding, when intestinal absorption had come to an end, was about 1.30 per thousand parts of the bodily weight; or, for the whole twenty-four hours, a little over 3 per cent. of the bodily weight. For a man of medium size, this would give not far from 2000 grammes as the average daily quantity of lymph alone.

Internal Renovation of the Animal Fluids.—By the combined actions of secretion, transudation, and reabsorption, a continual interchange or renovation of the animal fluids takes place in the living body, which is dependent for its materials upon the circulation of the blood, and which may be considered as a kind of secondary circulation through the substance of the tissues. For all the digestive fluids, as well as the bile discharged into the intestine, are reabsorbed in the natural process of digestion and again enter the current of the circulation. These fluids, therefore, pass and repass through the mucous membrane of the alimentary canal and adjacent glands, becoming more or less altered in con stitution at each passage, but still serving to renovate alternately the constitution of the blood and the ingredients of the digestive secretions. The elements of the blood itself also transude in part from the capillary vessels, and are again taken up from the tissues by the lymphatics, to be finally restored to the venous blood, in the immediate neighborhood of the heart.

The daily quantity of all the fluids thus transuded and reabsorbed will serve to indicate the activity of endosmosis and exosmosis in the living body. In the following table, the quantities are all estimated,

from preceding data, for a man of medium size.

Not less than 8000 grammes therefore of the animal fluids, a quantity equal to that of the entire blood and amounting to more than 12 per cent. of the weight of the whole body, transude through the internal membranes and are restored to the blood by reabsorption, in the course of a single day. It is by this process that the natural constitution of the parts, though constantly changing, is still maintained in its normal condition, through the movement of the circulating fluids and the renovation of their materials.

CHAPTER XVII.

THE URINE.

THE urine is distinguished from all the other animal fluids by the fact that it represents only the products of the waste or physiological disintegration of the body. The living body, while in the active performance of its functions, is the seat of various manifestations of force, such as animal heat, sensibility, and motion, which are the indications of its vitality. These manifestations of force, in the living organism, as well as elsewhere, are only produced at the expense of its materials, and by their change of state or metamorphosis in the internal process of nutrition. It is accordingly an essential condition of the existence and activity of the animal body that it should go through with an incessant transformation and renewal of its component parts. Every living being absorbs more or less constantly certain nutritive materials from without, which are modified by assimilation and converted into the natural ingredients of its tissues. At the same time with this continuous process of growth and supply, there goes on an equally continuous change, by which the elements of the organized frame pass over into new forms of combination, destined to be expelled from the body as the products of its disintegration.

Certain substances, therefore, are constantly making their appearance in the animal tissues and fluids, which were not introduced with the food, but which have been produced in their interior by the process of continued metamorphosis. These substances result from the new combinations taking place in the organized frame. They are the forms under which those materials present themselves which have once made part of the animal tissues, but which have become altered by the incessant changes characteristic of living beings, and which are consequently no longer capable of exhibiting vital properties, or of aiding in the performance of the vital functions. The process of the elimination and removal of these materials is called excretion, and the materials themselves are known as the excrementitious substances.

These substances have peculiar characters by which they are distinguished from other ingredients of the living body. They are crystallizable and for the most part soluble in water, at least in the form under which they appear in the excreted fluids. They are formed in the blood or in the substance of the tissues from which they are absorbed by the blood, and are conveyed by the circulating fluid to the excretory organs through which they are discharged. If their elimination from the body be in any way arrested or impeded, their accumulation in the system produces a disturbance of the vital functions, which is more or

less severe according to their special character and the rapidity of their production. This poisonous influence is especially manifested in its action upon the nervous system, causing an abnormal irritability, derangement of the special senses, delirium, insensibility, coma, and death. These effects are more particularly marked in the case of urea after suppression of the urine; a complete stoppage of the elimination of this substance in the human subject usually producing a fatal result in three or four days.

The excrementitious matters, however, are not to be considered as poisonous, or even deleterious, in the quantities in which they normally occur in the animal solids and fluids. On the contrary, they are the natural products of the functional activity of the animal system, and are, therefore, as essential to the continued manifestation of life as the nutritious materials supplied by the food. It is only when the regular course of their elimination is retarded that they interfere with the due performance of the functions, by deranging the natural constitution of the tissues.

A variety of excrementitious substances are produced in the body, some of which are probably eliminated, in small proportion, with the perspiration or with the feces. The carbonic acid, exhaled in large quantity from the lungs, is to be regarded as belonging to this class, since it is produced in the substance of the tissues and constantly discharged by respiration. But the most important substances, usually included under the head of excrementitious matters, are distinguished by the fact that they contain nitrogen as one of their ultimate elements, and that they otherwise exhibit a remarkable analogy with each other in their chemical composition. They accordingly form a natural group of organic substances, resembling each other in their origin, their constitution, and their physiological destination. They are furthermore associated together by the circumstance that they are all eliminated from the body by the urine, of which they form the essential and characteristic ingredients.

The urine is therefore the only animal fluid which is solely an excretion. It is a solution of the nitrogenous excrementitious matters of the animal frame; and by its abundance and composition it indicates the activity of the healthy metamorphosis of the organic tissues and fluids. Beside its nitrogenous ingredients, it contains also most of the mineral salts which are discharged from the body; and by the water which holds these solid matters in solution it forms the channel for a large proportion of the fluids passing daily through the system. Furthermore, accidental or abnormal ingredients, introduced into the blood, almost invariably find their way out of the system by the kidneys, and thus appear as temporary ingredients of the urine. The constitution and physiological variations of this fluid during health, and its alteration in disease, are regulated by the corresponding changes of nutrition or activity in the body at large. The urine is therefore one of the most essential products of the animal system, and its formation is second in importance only to the function of respiration.

Physical Properties of the Urine.

The urine is a clear, amber-colored fluid, of a watery consistency, and with a distinctly acid reaction. As a general rule, its transparency is so nearly perfect that no appearance of turbidity is perceptible by ordinary diffused daylight. It contains, however, a very small quantity of mucus from the urinary bladder, which may be rendered visible as a faint opalescence when a sunbeam is made to pass through it in a lateral direction. If the urine be allowed to remain at rest for a few hours in a cylindrical glass vessel, the mucus gradually subsides, forming a very light cloudy mass at the bottom and leaving the supernatant fluid entirely clear. The ingredients of the urine itself are all therefore in a state of complete solution. While still warm and fresh, the urine has a peculiar but not offensive odor, which disappears on cooling and may be then restored by gentle heating. The average specific gravity of healthy urine, in the adult, is from 1020 to 1025; and its daily quantity is about 1200 cubic centimetres.

Variations of the Urine in Quantity, Acidity, and Specific Gravity. -The urine does not present uniformly the same characters, but varies normally from hour to hour, in each individual, at different periods of the day. It is usually discharged from the bladder five or six times in the twenty-four hours, and each specimen shows more or less variation in its physical properties. This variation depends upon the changing conditions of the body, as to rest, exercise, food, drink, sleeping, and waking. In the same person, leading a uniform mode of life from day to day, the diurnal variations of the urine follow each other with great regularity; although in different persons, whose habits are different, they may not be altogether the same. As a general rule, the urine which collects in the bladder during the night and is first discharged in the morning is strongly colored, of high specific gravity, and has a very distinct acid reaction. That passed during the forenoon, on the other hand, is pale and of comparatively low specific gravity; often falling so low as 1018 or even 1015. At the same time, its acidity diminishes or even disappears altogether; so that at this time in the day the urine is frequently neutral or slightly alkaline. Toward noon, its density and depth of color increase, and its acidity returns. All these properties become more strongly marked during the afternoon and evening; and toward night the urine is again deeply colored and strongly acid, and has a specific gravity of 1028 or 1030.

The following instances will serve to show the general characters of this variation: