of supporting the powers of the body by judiciously-devised means, and of aiding the elimination of the morbid matter through the lungs and skin by a copious supply of pure air, than of interfering more actively to promote that which Nature is already effecting in the most advantageous manner.

753. In like manner, the Liver is charged with the separation of hydrocarbon, in a fluid form; for which a supply of oxygen is not requisite. This product is partly derived from the waste of the system; but the arrangement of the biliary vessels leads to the belief, that part of it may be at once derived from crude matter, taken up by the mesenteric veins, and eliminated from them by the hepatic cells, without ever passing into the general circulation. And various facts seem to indicate, that the Liver is also destined to remove from the blood extraneous substances, which are noxious to it. Thus, in cases where death has resulted from the prolonged introduction of the salts of Copper into the system, a considerable amount of that metal has been obtained from the substance of the gland.

Fig. 131.

754. It has been already pointed out (§ 726), that in those tribes of animals whose respiration is feeble, a considerable part of the mass of the liver is composed of fatty matter; and this condition may be induced, as a state of disease, in warm-blooded, energetically-respiring Birds and Mammals, by impediments to the due performance of the respiratory process. This is remarkably shown in the treatment of the geese which are to furnish the celebrated Strasburg patés. The unfortunate bird is closely confined at a high temperature; so that the respiration is reduced to its minimum amount, by the combined effects of warmth and muscular inaction; and it is then crammed with maize, which contains a large amount of oily matter. The consequence is, that its liver soon enlarges, and becomes unusually fatty; its cells being gorged with oil-globules, instead of each containing no more than one or two and it is then ready for the epicureans who set so high a value on the paté de foie gras. A similar diseased condition of the liver frequently presents itself in Man, in connexion with chronic disorders of the respiratory organs, which diminish the amount of hydrocarbon eliminated through their agency; this "fatty liver" is peculiarly common in the advanced stages of Phthisis. It may arise, however, from a local disorder of nutrition, such as that which produces the fatty degeneration of other organs. Such a fatty degeneration may occur in the Kidney, for example, as a consequence of inflammation of its tissues.

Hepatic Cells gorged with fat: -a, atrophied nucleus; b, adipose globules.

755. With regard to the Kidneys, it has been already pointed out that they are the special emunctories of the azotized products of the decomposition of the tissues; and that they serve also to convey away the overplus of such earthy and alkaline salts, as are readily soluble. Moreover, it has been shown that the surplus proteine-compounds, which are not required for the nutrition of the system, must be excreted by their agency, after having been metamorphosed into urea. And we have now to notice, that other matters of an injurious charac

ter, whether introduced from without, or generated within the system, are drawn off by the same channel. Thus the saline compounds, taken up by the absorbent process (§ 493), are for the most part set free through these organs; especially when their properties are such, as to excite the action of the kidneys in a peculiar degree. Thus, Prussiate of Potash has been detected in the urine, within one minute after it has been introduced into the stomach. It has been sometimes noticed that Iodide of Potassium, when administered as a medicine, is retained within the body for some days, producing extensive cutaneous eruptions, or some other unusual consequence; and that it then suddenly begins to pass off by the kidneys, and is excreted in very large quantities. Further, it has been shown by Dr. Letheby, that poisonous substances (such as arsenious acid), introduced into the system in small but frequently-repeated doses, may be carried out of the body with such rapidity as to be prevented from exerting their injurious effects, provided that diuretics be administered at the same time. The effect of the inhalation of the vapor of turpentine, even in a very diluted state, in speedily imparting to the urine the odor of violets, is an evidence that not merely the actual substances imbibed, but new and peculiar compounds to which they give rise, are thus eliminated by the Kidneys.

756. The most singular variations in the excretory function of the Kidneys are seen, however, when the Urine is charged with substances which are not only foreign to it, but are altogether foreign to the healthy body. The most remarkable instance of this is seen in the disease termed Diabetes, in which a large quantity of Sugar is formed, either directly from the food, or by the disintegration of the solid tissues; and in which this compound is eliminated by the Kidneys, imparting to the urine a saccharine taste. And another example of the same general fact is seen in the "oxalic diathesis," in which an unusual arrangement of the elements that usually form urea or uric acid, gives rise to a new and peculiar compound, oxalate of ammonia; this being drawn off by the kidneys, and being decomposed by the calcareous matter present in the urine, gives rise to a deposit of oxalate of lime. In the treatment of such diseases, our attention must be given, not so much to the secreting organ, as to the condition of the system at large, of which the character of the secreted product is the indication or exponent.

757. To what has already been stated in regard to the exhalant functions of the Lungs and Skin, it may be added that many states of disease are marked by an unusual odor emitted from the body; and there can be little doubt that the peculiar odorous matter is pre-formed in the blood, as we know that the ordinary scent of any species (whether Man, Dog, Horse, Goat, &c.) may be set free from the blood of that species, by the addition of sulphuric acid. The existence of such odors, therefore, is not to be attributed to disordered function in the excreting organs; but to the formation of morbid products in the interior of the body, which these organs do their best to remove. The foetid breath, which frequently accompanies an attack of indigestion, is another instance of the power of the lungs to eliminate, not merely

Carbonic acid, but other products of the changes in composition which the food undergoes when introduced into the system.

758. The same remarks apply, and with yet greater force, to the Intestinal glandule; whose function it is, not merely to remove the putrescent matter ordinarily formed by the disintegration of the tissues, or by the decomposition of unassimilated food, but also to draw off the still more offensive products of such changes as take place in disease. Thus there are conditions of the system, in which, without any well-marked disorder, the fæces emit a peculiarly foetid odor; and with these is almost always associated a depressed state of mind. Now it can scarcely be doubted, that the real fault is here rather in the early part of the nutritive operations, than in the excretory function; and that the foetor of the contents of the intestine depends upon the undue formation of putrescent matter in the system, which, by tainting the blood, causes its action upon the brain to become unhealthy. The object of the physician will be here to eliminate the morbid product, by the moderate use of purgatives; and so to regulate the diet and regimen, as to correct the tendency to its formation.-An excessive foetor in the evacuations, as well as in the exhalations from the skin and lungs, is peculiarly characteristic of those very severe forms of typhus (now, happily, of comparatively rare occurrence), which are termed putrid fevers. Here the whole of the solids and fluids of the body appear to have an unusual tendency to decomposition, in consequence of the introduction of some morbid agent, which acts as a ferment; and the system attempts to free itself from the products of that decomposition, by the various organs of excretion, particularly the Skin and Intestinal surface.

759. It is of great importance that the Student should form clear conceptions on this subject; and that he should not (as too often happens), by directing his remedies to the mere symptoms or results of a disease, act in precise opposition to the natural tendency of the system to free itself from some unusual noxious matter, through those channels which are ordinarily destined to carry off only the regular products of its disintegration.

CHAPTER X.

OF THE DEVELOPMENT OF HEAT, LIGHT, AND ELECTRICITY, IN THE ANIMAL BODY.

760. It has been shown, in an earlier part of this volume (CHAP. II.), that all Vital actions require a certain amount of Heat for their performance; and that there is a great variety amongst the different classes of Animals, both in regard to the degree of Heat which is most favorable to the several processes of their economy, and in regard to their own power of sustaining it, independently of oscillations in the

temperature of the surrounding medium. As a general rule, the Invertebrated animals are cold-blooded; that is, they have little or no power of sustaining an independent temperature. The degree of energy of their vital actions entirely depends, therefore, upon the warmth they receive from the air or water they inhabit; they have no power of resisting the depressing influence of cold; and they are generally so organized, as to pass into a state of complete inaction or torpidity, when the temperature sinks below a certain point,-after gradually becoming more and more inert with every diminution in the heat of their bodies. The same is true, also, of most Fishes and Reptiles: but the animals of the former class, from the more equable temperature of the medium they inhabit, are not so liable to be reduced to inaction as the latter; being usually so organized, as to retain their activity so long as the water around them continues liquid; and being actually imbedded in a frozen state, when the water around them is converted into ice, without the loss of their vitality. There are certain Fishes, however, such as the Thunny, Sword-fish, and other large species of the Mackerel tribe,-which are able to sustain a temperature considerably above that of the sea they inhabit; thus in the Bonito, the heat of the body has been found to be 99°, when the temperature of the surrounding sea was but 8010. It is not probable, however, that the temperature of the body would be kept up to the same standard, if that of the sea should be considerably lowered; but it would proba bly remain at from 18° to 20° above the latter. And in like manner, it has been noticed that many of the more active Reptiles possess the power of sustaining the temperature of their bodies at 10° or 15° above that of the surrounding air.

761. The classes of animals which are especially endowed with the power of producing and maintaining heat, are Insects, Birds, and Mammalia. The remarkable variations which present themselves in the temperature of the first of these classes, and the connexion of these variations with the condition of the animals in regard to activity or repose, have already been sufficiently noticed (§ 123). The temperature of Birds is higher than that of any other class of animals; varying from 100° to 111 or 112°. The lowest degree is found in some of the aquatic species, as the Gull, and in those which principally live on the ground, as the Fowl tribe; and the highest in the birds of most active flight, as the Swallow. The temperature of the Mammalia seems to range from about 96° to 104°; that of Man has been observed as low as 9610, and as high as 102°. The variations are dependent in part upon the temperature of the external air; but are influenced also by the general condition of the body as to repose or activity, the period of the day, the time that has elapsed since a meal, &c. A somewhat larger amount of caloric is generated during the day, than in the night; and the body is usually warmer, by a degree or two, at noon, than at midnight. There is also a slight increase during the digestion of a meal; and exercise is a powerful means of raising the temperature.The range of temperature is much greater in disease; thus the thermometer has been seen to rise to 106° in Scarlatina and Typhus, and to

110° in Tetanus; whilst it has fallen to 82° in Spasmodic Asthma, and to 77° in Cyanosis and Asiatic Cholera.

762. In searching for the conditions on which this production of heat within the Animal body is dependent, it is very important to bear in mind, that a similar generation of Caloric may be observed in the Vegetable kingdom. It appears from the most recent and exact experiments, that all living Plants are somewhat warmer than similar dead plants exposed to the same atmosphere; and that the elevation is the greatest in the leaves and young stems, in which the most active vital changes are taking place. But the most decided production of heat occurs in the flowering of certain Plants, such as the Arum, which have large fleshy receptacles, on which a great number of blossoms are crowded; thus a thermometer placed in the centre of five spadixes of the Arum cordifolium has been seen to rise to 111°, and one placed in the midst of twelve spadixes has risen to 121°, whilst the temperature of the surrounding air was only 66°. In the germination of seeds, also, a great elevation of temperature occurs, which is rendered most evident by bringing together a number of seeds, as in the process of malting, so that the caloric is not dissipated as fast as it is generated; the thermometer, placed in the midst of a mass of seeds in active germination, has been seen to rise to 110°.

763. Thus it is evident that the chemical changes which are involved in the operations of Nutrition, are capable of setting free a large amount of heat; which, although ordinarily dissipated from the vegetating surface too speedily to manifest itself, becomes sensible enough, when this rapid loss is checked. If we further examine into the nature of the chemical changes which appear most concerned in this elevation of temperature, we find that they uniformly consist in the combination of the carbon of the plant with the oxygen of the atmosphere; so that a large quantity of carbonic acid is formed and set free, precisely in the manner of the Respiration of Animals. This process is so slowly performed, in the ordinary growth of Plants, that it is concealed (as it were) by the converse change,-the fixation of carbon from the carbonic acid of the atmosphere, under the influence of light (§ 83). But it takes place with extraordinary energy during flowering and germination; a large quantity of carbon being set free, by union with the oxygen of the air; and the starchy matter of the receptacle, or of the seed, being converted into sugar. Now it has been ascertained by careful experiments, that the amount of heat generated is in close relation with the amount of carbonic acid set free; and that, if the formation of the latter be prevented, by placing the flower or the seed in nitrogen or hydrogen, no elevation of temperature takes place; whilst, if the process be stimulated by pure oxygen, so that a larger proportion of carbonic acid is evolved, the elevation of temperature is more rapid and considerable than usual.

764. Upon examining into the conditions under which Caloric is generated in the Animal body, we find them essentially the same. Wherever the temperature of the body is maintained at a regular standard, so as to be independent of variations in the warmth of the surrounding medium, we find a provision for exposing the blood most freely to the in