3. The excretions by the bowels are, properly speaking, only those parts of the alvine evacua tions, which are secreted within the body itself, and mixed with the residue of the food. It is probable that part of the secretions from all parts of the primm vise are thus excreted, but the only one of which it has been ascertained that it is, in part at least, destined necessarily for excretion, is the bile. It is certain that the peculiar animal matter of this secretion, (re garded by some as of pretty simple and by others as of very complicated composition) is never found in the healthy state in the lacteal vessels or thoracic duct—that it is found in full quantity along with the residue of the aliments in the lower intestines,—that it is increased in quantity when the excretion of urine is sup pressed in animals by extirpation of the kid neys; and again, that when this secretion is sup pressed, the urine is increased and altered ; and we can therefore have no difficulty about regard ing this part of the bile as strictly an excretion, notwithstanding that we have good evidence, that at least the alkali of the bile is of use in the digestion and assimilation of the food. Of the quantity of matter strictly excreted from the intestines in the day it must of course be very difficult to judge. chemical elements that escape in the biliary matter must be chiefly carbon and hydrogen.
4. The urine is the most complex of the ex cretions, particularly as to saline impregnation, containing not only the salts which are detected in the blood, but a portion of every earthy and saline matter that can be found in any part of the body, besides the peculiar and highly azo tised animal matters, lithic acid and urea. The average quantity of urine passed in twenty-four hours may be about forty ounces, but is very liable to variation, particularly by temperature, being generally greater, as the excretion by the skin is less. The quantity of solid matter, animal, earthy, and saline, that passes off in this way has been stated at about fifteen drachms on an average, and is evideotly much less liable to change, the density of urine, in the healthy state, always diminishing as its quantity increases, and vice versa. The milk, and the semen, although destined to no useful office in the system in which they are formed, are rather to be called recrementitious secretions than excretions. Yet the former has this property in common with excretions, that its retention within the body, when the conditions of its formation exist, is hurtful. The menstrual discharge may be regarded as strictly an excretion, though one which is required only in the human species and for a limited time.
Ikrzelius stated several distinctions, which he thought important, between the excremen titious and recremcntitious secretions in the animal body, particularly that the former are always acid, that each of them contains more than one animal matter, and that their salts are more numerous and varied than those in the blood, while the latter have an excess of alkali from the same saline ingredients as the serum of the blood, and each contains only a single animal principle, substituted for the albumen of the serum. But these distinctions are cer
tainly inapplicable in several instances, and the only one of them which appears to be a general fact, is the more complex saline impregnation of the excreted fluids.
III. It is unnecessary to dwell on the well known injurious effects, on the animal ceconomy, of the suppression of any of these excretions. It may, indeed, reasonably be doubted, whether the rapidly fatal effects of obstructing the ex posure of the blood to the air at the lungs are owing to the retention of carbon, or carbonic acid ; it seems much more probable that the cause which stops the circulation at the lungs in asphyxia, is the suspension of the absorption of free oxygen into the blood, rather than the suspension of the evolution of carbon or car bonic acid. But even if the circulation could be maintained, after the exposure of the blood to the air is suspended, we know that the carbonic acid which we have good reason to believe would soon be in excess in the blood, would then act as a narcotic poison. Of the effects of suspension of the excretion by the skin we can not speak with certainty, because that is a case which probably hardly ever occurs ; and if it were to occur, the lungs and kidneys would probably act as perfect succedanea. But it is worthy of notice that at a time when the skin is known to be nearly unfit for its usual functions —during the desquamation that succeeds exan thematous diseases, and especially scarlatina,— the lungs and the kidneys, on which an unusual burden may thereby be supposed to be thrown, arc remarkably prone to disease. The effect of suppression of the excretion of urine (i. e. of ischuria renalis), whether occurring as a disease in man, or produced by extirpation of the kid neys in animals, is uniformly more or less of febrile symptoms quickly followed by coma and death ; and in these circumstances it is now known, that the urea may be detected in the blood. A variety of morbid affections, and particularly an affection of the nervous system marked by inaptitude for muscular or mental exertion, always follows the obstruction of the excretion of bile, and absorption of bile into the blood constituting jaundice.