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secreted, which is spread over the articular surfaces of the bones, and facilitates their movements.

Havers considered this fluid to be secreted by synovial glands, for such he conceived the reddish cellular masses to be, that are found in certain articulations. Haller, again, strangely regarded the synovia as the marrow, that had transuded through the spongy extremities of the bones; but, since the time of Bichat, every anatomist and physiologist has ascribed it to the exhalant action of the synovial membrane, which strongly resembles the serous membranes in form, structure and functions, and whose folds constitute the projections, which Havers mistook for glands.

This membrane exists in all the movable articulations, and in the channels and sheaths in which the tendons play. The generality of anatomists regard the articular capsules as shut sacs; the membrane being reflected over the incrusting cartilages. Magendie, however, affirms, that he has several times satisfied himself, that the membranes do not pass beyond the circumference of the cartilages.

From the inner surface of these membranes, the synovia is exhaled, precisely in the same manner as in other serous cavities.

Margueron analyzed the synovia, obtained from the lower extremity of the ox, and found it to consist of fibrous matter, 11.86; albumen, 4.52; muriate of soda, 1.75; soda, 0.71; phosphate of lime, 0.70; and water, 80.46.

6. Exhalation of the Colouring Matter of the Skin and of other parts.

The nature of the exhalation, which constitutes the colouring matter of the rete mucosum, has already engaged our attention, when treating of the skin under the sense of touch. It is presumed to be exhaled by the vessels of the skin, and to be deposited beneath the cuticle, so as to communicate the colours that characterize the different races. Such are regarded as the secretory organs by most anatomists and physiologists; but Gautier, whose researches into the intimate constitution of the skin have gained him much celebrity, is of opinion, that it is furnished by the bulbs of the hair; and he assigns, as reasons for this belief, that the negro, in whom it is abundant, has short hair; that the female, whose hair is more beautiful and abundant than that of the male, has the fairest skin; and that when he applied blisters to the skin of the negro, he saw the colouring matter oozing from the bulbs of the hair, and deposited at the surface of the rete mucosum.

The composition of this pigment cannot be determined with precision, owing to its quantity being too small to admit of examination. Chlorine deprives it of its black hue, and renders it yellow. A negro, by keeping his foot for some time in water, impregnated with this gas, deprived it of its colour, and rendered it nearly white;

but, in a few days, the black colour returned with its former intensity. This experiment was made with similar results on the fingers of a negro.

Blumenbach, as is noticed elsewhere, thought, that the mucous pigment was formed chiefly of carbon; and his notion has received favour with many.

The uses of this pigment, as well as of that which lines the choroid coat of the eye, the posterior surfaces of the iris, and of the ciliary processes, are detailed in another place.

7. Areolar Exhalation.

Under this term, Adelon has included different recrementitial secretions effected within the organs of sense, or in parenchymatous structures, as the aqueous, crystalline, and vitreous humours of the eye, and the liquor of Cotugno, all of which have already engaged attention, the exhalation of a kind of albuminous, reddish, or whitish lymph into the interior of the lymphatic ganglions, and into the organs, called, by Chaussier, glandiform ganglions, and by Beclard, sanguineous ganglions;—viz: the thymus, thyroid, suprarenal capsules, and spleen. We know but little, however, of the fluids, formed in these various parts. They have never been analyzed, and their uses are inappreciable.

By some physiologists, a fluid is supposed to be exhaled from the inner coat of the arterial, venous, and lymphatic vessels. Not only, however, are we unaware of the nature of this fluid, but its very existence is doubted. Its use is presumed to be, to lubricate the interior of the vessel, and to prevent adhesion between it and the fluid circulating within it.

The following belong to the external exhalations.

8. Cutaneous Exhalation or Transpiration.

A transparent fluid is constantly exhaled from the skin, which is generally invisible, in consequence of its being converted into vapour as soon as it reaches the surface; but, at other times, owing to augmentation of the secretion, or to the air being loaded with humidity, it is apparent on the surface of the body.

When invisible, it is called the insensible transpiration or perspiration; when perceptible, sweat.

In the state of health, according to Thenard, this fluid reddens litmus paper; yet the taste is rather saline, resembling that of common salt, than acid.

Its smell is peculiar, and becomes almost insupportable when concentrated, and especially when subjected to distillation. It is composed, according to Thenard, of much water, a small quantity of acetic acid, muriate of soda, and perhaps of potassa, a very little

earthy phosphate, a trace of oxide of iron, and an inappreciable quantity of animal matter. Berzelius regards it as water, holding in solution the muriates of potassa and soda, lactic acid, lactate of soda, and a little animal matter.

Numerous experiments have been instituted for the purpose of discovering the quantity of transpiration that takes place in a given time. Of these, the earliest were by Sanctorius, for which he is more celebrated than for any other of his labours. For thirty years, this indefatigable experimentalist weighed daily, with the greatest care, his solid and liquid ingesta and egesta, and his own body, with the view of deducing the loss sustained by the cutaneous and pulmonary exhalations. He found, that every twenty-four hours, his body returned sensibly to the same weight, and that he lost the whole of the ingesta;—five-eighths by transpiration, and three-eighths by the ordinary excretions. For eight pounds of ingesta, there were only three pounds of sensible egesta, which consisted of forty-four ounces of urine, and four of fæces.

It is lamentable to reflect, that so much time was occupied in the attainment of such insignificant results. The self-devotion of Sanctorius, gave occasion, however, to the institution of numerous experiments of the same kind; as well as to discover the variations in the exhalation, according to age, climate, &c. The results of these have been collected by Haller, but they afford little instruction; especially as they were directed to the transpiration in general, without affording us any data to calculate the proportion exhaled from the lungs to that constantly taking place by the cutaneous surface.

Rye, who dwelt in Cork, lat. 51° 54', found, in the three winter months,—December, January, and February—that the quantity of urine was 3937 ounces; of the perspiration, 4797: in the spring months—March, April, and May—the urine amounted to 3558; the perspiration to 5405: in the summer months of June, July, and August, the urine amounted to 3352; the perspiration to 5719: and in the three autumnal months—September, October, and November -the quantity of urine was 3369: that of the perspiration 4471. The daily average estimate in ounces was as follows:

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thus, making the average daily excretion of urine, throughout the year, to be a little more than 39 ounces; and of the transpiration, 56 ounces.

Keill, on the other hand, makes the average daily perspiration, 31 ounces; and that of the urine 38; the weight of the fæces being

His

5 ounces, and that of the solid and liquid ingesta, 75 ounces. experiments were made at Northampton, England, lat. 52° 11'.

Bryan Robinson found, as the result of his observations in Ireland, that the ratio of the perspiration to the urine was, in summer, as 5 to 3; in the winter as 2 to 3; whilst in April, May, October, November, and December, they were nearly equal. In youth, the ratio of the perspiration to the urine, was as 1340 to 1000; in the aged, as 967 to 1000.

Hartmann, when the solid and liquid ingesta amounted to 80 ounces, found the urine discharged 28 ounces; the fæces 6 or 7 ounces; and the perspirable matter, 45 or 46 ounces. Von Gorter, in Holland, when the ingesta were 91 ounces, found the perspiration to amount to 49 ounces; the urine to 36; and the fæces to 8.

Dodart asserts, that in France, the ratio of the perspiration to the fæces, is as 7 to 1; and to the whole egesta as 15 to 12 or 10. The average perspiration, in the twenty-four hours, he estimates at 33 ounces and 2 drachms; and Sauvages, in the south of France, found, that when the ingesta were 60 ounces in the day, the transpiration amounted to 33 ounces; the urine to 22; and the fæces to 5.

Most of these estimates were made in the cooler climates,—the "regiones boreales,"—as Haller has, not very happily, termed them.

December,

January,

February,

According to Lining, whose experiments were made in South Carolina, lat. 32° 47', the perspiration exceeded the urine in the warm months; but in the cold, the latter had the preponderance. The following table gives the average daily proportion of the urine and perspiration, for each month of the year, in ounces, as quoted by HALLER.

March,

April,
May,

June,

July,
August,
September,
October,
November,

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After the period at which Haller wrote, no experiments of any moment were adopted for appreciating the transpiration. Whenever trials were instituted, the exhalation from both the skin and the lungs was included in the result, and no satisfactory means were adopted for separating them, until Lavoisier and Seguin made their celebrated experiments.

SEGUIN inclosed himself in a bag of gummed taffeta, which was tied above the head, and had an aperture, the edges of which were fixed around the mouth by a mixture of turpentine and pitch. By means of this arrangement, the pulmonary transpiration alone escaped into the air. To estimate its quantity, it was merely necessary for M. Seguin to weigh himself in the sack, in a very delicate balance, at the commencement and termination of the experiment. By repeating the experiment out of the sack, he determined the total quantity of the transpired fluid; so that, by deducting from this the quantity of fluid exhaled from the lungs, he obtained the amount of the cutaneous transpiration. He, moreover, kept an account of the food, which he took; of the solid and liquid egesta; and, as far as he was able, of every circumstance that could influence the transpiration.

The results, at which Lavoisier and Seguin arrived by a series of well-devised and well-conducted experiments were the following:

First. Whatever may be the quantity of food taken, or the variations in the state of the atmosphere, the same individual, after having increased in weight by the whole quantity of nourishment taken, returns daily, after the lapse of twenty-four hours, to nearly the same weight as the day before; provided he be in good health; his digestion perfect; that he is not fattening, or growing; and that he avoids all kinds of excess.

Secondly. If, when all other circumstances are identical, the quantity of food varies; or if the quantity of food being the same -the effects of transpiration differ; the quantity of the excrements augments or diminishes, so that every day, at the same hour, we return nearly to the same weight;--proving that when digestion goes on well, the causes, that concur in the loss or excretion of the food taken in, afford each other mutual assistance;—in the state of health one charging itself with what the other is unable to accomplish.

Thirdly. Defective digestion is one of the most direct causes of the diminution of transpiration.

Fourthly. When digestion goes on well, and the other causes are alike, the quantity of food has but little effect on the transpiration. Seguin affirms, that he has very frequently taken, at dinner, two pounds and a half of solid and liquid food; and, at other times, four pounds, yet the results, in the two cases, differed but little from each other; provided only, that the quantity of fluid did not vary materially in the two cases.

Fifthly. Immediately after dinner, the transpiration is at its minimum.

Sixthly. When all other circumstances are equal, the loss of weight, induced by insensible transpiration, is at its maximum during digestion. The increase of transpiration, during digestion, compared with the loss sustained when fasting is, at an average, 28 grains per minute.

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