Abbildungen der Seite
PDF
EPUB

lowed, with more or less modification, by Plenck, Richerand, Blumenbach, Young, and Bostock: the last of whom, the most recent writer, has eight classes:—the aqueous, albuminous, mucous, gelatinous, fibrinous, oleaginous, resinous, and saline. To all of these classifications, cogent objections may be made. The one we shall follow is the anatomical, not because it is the most perfect, but because it is the course, that has been usually adopted throughout this work.⁕

Sect. I.—Of the Exhalations.

All the exhalations occur in the areolæ or internal cavities of the body, or from the skin and mucous membranes:—hence their division into internal and external. The former are all recrementitial; the latter recremento-excrementitial. To the class of internal exhalations belong; 1. The serous exhalation. 2. The serous exhalation of the cellular membrane. 3. The adipous exhalation of the cellular membrane. 4. The exhalation of the marrow. 5. The synovial exhalation. 6. The exhalation of the colouring matter of the skin, and of other parts; and 7. The areolar exhalation. To the class of external exhalations belong; 1, that of the skin, or cutaneous transpiration. 2. The exhalation of the mucous membranes.

1. The Serous Exhalation.

This is the fluid secreted by the serous membranes that line the various cavities of the body; as the pleura, pericardium, peritoneum, arachnoid coat of the brain, and tunica vaginalis testis.

From these membranes a fluid is exhaled, which is of an albuminous character, considerably resembling the serum of the blood except in containing less albumen.

In the healthy condition, this fluid never accumulates in the cavities; the absorbents taking it up in proportion as it is deposited; but if, from any cause, the exhalants should pour out a larger quantity than usual, whilst the absorbents are not proportionably excited, accumulation takes place; or the same effect ensues if the exhalants pour out no more than their usual quantity, whilst the absorbents do not possess their due activity. Under either circumstance, we have accumulation or dropsy; and, accordingly, dropsy may be either active or passive.

The exhaled fluid probably transudes through the parietes of the arteries, and reenters the circulation by imbibition through the coats of the veins. If we kill an animal and open it immediately afterwards, this exhalation appears in the form of a halitus or vapour, and the fluid is seen lubricating the free surface of the membrane.

For an enumeration of the different fluids or humours of the body, see Vol. I.

This, indeed, appears to be its principal office; by which it favours the motion of the organs upon each other.

The serous exhalations probably differ somewhat in each cavity, or according to the precise structure of the membrane. The difference between the chymical character of the fluid of the dropsy of different cavities would lead to this belief. As a general rule, according to Dr. Bostock, the fluid from the cavity of the abdomen contains the greatest proportion of albumen, and that from the brain the least; but many exceptions occur to this.

2. Serous Exhalation of the Cellular Membrane.

The cellular membrane, wherever existing, is kept moist by a serous fluid, analogous to that exhaled from serous membranes, and which appears to have the same uses,—that of facilitating the motion of the lamellæ or plates on each other, and consequently of the organs, between which the cellular tissue is placed.

When this secretion collects, from the causes mentioned in the last section, the disease, called oedema or anasarca, is induced.

3. Adipous Exhalation of the Cellular Membrane.

Considerable diversity of opinion has prevailed regarding the precise organ of the secretion of fat. Haller supposed that the substance exists ready formed in the blood, and that it simply transudes through the pores of the arteries; and Chevreul has given some countenance to this opinion, by the circumstance of his having met with a fatty matter in that fluid.

Anatomists have, likewise, been divided upon the subject of the precise tissue into which the fat is deposited; some believing it to be the ordinary cellular tissue, into which it is dropt by the agency of appropriate vessels; others, as Malpighi and William Hunter, believing in the existence of a peculiar adipous tissue, consisting, according to Beclard, of small bursæ or membranous vesicles, which inclose the fat, and are found situated in the areolæ of the cellular tissue. These vesicles are said to vary greatly in size: generally, they are round and globular; and, in certain subjects, receive vessels, that are very apparent. These vesicles form so many small sacs without apertures, in the interior of which are filaments arranged like septa. In fatty subjects, these adipous vesicles are very perceptible, being attached to the cellular tissue and neighbouring parts by a vascular pedicle.

The arrangement of this tissue, as well as the quantity of fat, varies in different parts of the body. It is always found in the orbit, on the sole of the foot, and at the pulps of the fingers and toes. The subcutaneous cellular tissue, and that covering the heart, kidneys, &c. also generally contain it; but it is never met with in the eyelids, scrotum, or within the cranium.

Fat is exhaled by the secretory vessels, in a fluid state; but, after it is deposited, it becomes more or less solid. According to the researches of Chevreul, human fat is almost always of a yellow colour; inodorous, and composed of two portions;—the one fluid, and the other concrete, which are themselves composed, but in different proportions, of two new immediate principles, to which that chymist gave the names elaine and stearine respectively.

It is probable, that chymical analysis would exhibit the fat to vary in different parts of the body, as its sensible properties are manifestly different. Sir Everard Home, on loose analogies and inconclusive arguments, has advanced the opinion, that it is more than probable, that fat is formed in the lower portion of the intestines, and from thence is carried, through the medium of the circulating blood, to be deposited in almost every part of the body. "When there is a great demand for it, as in youth, for carrying on growth, it is laid immediately under the skin, or in the neighbourhood of the abdomen. When not likely to be wanted, as in old age, it is deposited in the interstices of muscular fibres, to make up in bulk for the wasting of these organs."

The uses of the fat are both general and local. The great general use is, by some physiologists, conceived to be,—to serve as a provision in cases of wasting indisposition; when the digestive function is incapacitated for performing its due office, and emaciation is the consequence. In favour of this view, the rapidity with which fat disappears after slight abstinence has been urged, as well as the facts, connected with the torpidity of animals, which are always found to diminish in weight during this state.

Professor Mangili of Pavia, procured two marmots from the Alps, on the first of December. The larger weighed 25 Milanese ounces; the smaller only 224th; on the third of January, the larger had lost 4ths of an ounce, and the smaller 17ths. On the fifth of February, the larger weighed only 227ths; the smaller 21.

Dr. Monro kept a hedge-hog from the month of November to the month of the March following, which lost, in the meanwhile, a considerable portion of its weight. On the 25th of December, it weighed 13 ounces and 3 drachms; on the 6th of February, 11 ounces and 7 drachms; and on the eighth of March, 11 ounces and 3 drachms. The loss was 13 grains daily.

The local uses of the fat are chiefly of a physical character. On the sole of the foot it diminishes the effects of pressure, and its use is the same on the nates: in the orbit, it forms a kind of cushion, on which the eyeball moves with facility; and when in certain limits, it gives that rotundity to the frame, which we are accustomed to regard as symmetry. In another place, it was observed, that fatty substances are bad conductors of caloric; and hence that it may tend to preserve the temperature of the body in cold seasons;—a view, which is favoured by the fact, that many of the arctic animals are largely supplied with fat beneath the common integuments; and it

has been affirmed, that fat people generally suffer less than lean from the cold of winter.

It is obviously impracticable to estimate, accurately, the total quantity of fat in the body. It has been supposed, that, in an adult male of moderate size, it forms th of the whole weight; but it is doubtful whether we ought to regard this as even an approximation; the data being so inadequate.

In some cases of polysarcia or obesity, the bulk of the body has been enormous. In the Philosophical Transactions, No. 185, the case of a girl is detailed, who weighed 256 pounds, when only four years old. A man of the name of Bright, at Maldon, England, weighed 728 pounds; and the celebrated Daniel Lambert, of Leicester, England, weighed 739 pounds a little before his death, which occurred in the fortieth year of his age. The circumference of his body was three yards and four inches; of his leg one yard and one inch. His coffin was six feet four inches long; four feet four inches wide; and two feet four inches deep.

In some of the varieties of the human family we meet with singular adipous deposits. In the Bosjesman female vast masses of fat accumulate on the buttocks, which give them the most extravagant appearance. The projection of the posterior part of the body, in one subject, according to Barrow, measured five inches and a half from a line touching the spine. "This protuberance," he remarks, "consisted of fat, and when the woman walked, had the most ridiculous appearance imaginable, every step being accompanied with a quivering and tremulous motion, as if two masses of jelly were attached behind."

The "Hottentot Venus," who had several projections, measured more than nineteen inches across the haunches; and the projection of the hips exceeded 63 inches. Dr. Somerville found, on dissection, that the size of the buttocks arose from a vast mass of fat, interposed between the integuments and muscles, which equalled four fingers breadth in thickness. It is singular, that, according to the statement of this female, which is corroborated by the testimony of Mr. Barrow, this deposition does not take place till the first pregnancy.

Pallas has described a variety of sheep—the ovis steatopyga or" fat-buttocked,"—which is reared in immense flocks by the pastoral tribes of Asia. In it, a large mass of fat covers the nates and occupies the place of the tail. The protuberance is smooth beneath, and resembles a double hemisphere, when viewed behind; the os coccygis or rump-bone being perceptible to the touch in the notch between the two. They consist merely of fat; and when very large, shake in walking like the buttocks of the female Bosjesman. Mr. Lawrence remarks, that there are herds of sheep in Persia, Syria, Palestine and some parts of Africa, in which the tail is not wanting as in the ovis steatopyga, but retains its usual length and becomes loaded with fat.

The circumstances, which favour obesity, are absence of activity and of excitement of all kinds; hence, for the purpose of fattening animals in rural economy, they are kept in entire darkness,—to deprive them of the stimulus of light, and to favour sleep and muscular inactivity. Castration—by abolishing one kind of excitability—and the time of life at which the generative functions cease to be exerted, especially in the female, are favourable to the same result.

4. Exhalation of the Marrow.

A fluid, essentially resembling fat, is found in the cavity of long bones, in the spongy tissue of short bones, and in the areolæ of bones of every kind. This is the marrow. The secretory organ is the very delicate membrane, which is perceptible in the interior of the long bones, lining the medullary cavity, and sending prolongations into the compact substance, and others internally, which form septa and spaces for the reception of the marrow. The cells, thus formed, are distinct from each other; and, from the observations of Howship, it would seem probable, that the oil of bones is deposited in longitudinal canals, that pass through the solid substance of the bone, and through which its vessels are transmitted. This oil of bones is the marrow of the compact structure, the latter term being generally restricted to this secretion, when contained in the cavities of long bones; that which exists in the spongy substance being termed by some writers, the medullary juice.

The medullary membrane, called also the internal periosteum, consists chiefly of blood-vessels ramifying on an extremely delicate cellular tissue, in which nerves may likewise be traced.

Berzelius examined marrow obtained from the thigh-bone of an ox, and found it to consist of the following constituents:—pure adipous matter, 96; skins and blood-vessels, 1; albumen, gelatine, extractive, peculiar matter and water, 3.

The marrow is one of the corporeal components, of whose use we can scarcely offer a plausible conjecture. It has been supposed to render the bones less brittle; but this is not correct, as those of the fœtus, which contain little or no marrow, are less brittle than those of the adult; and the bones of old persons, in which the medullary cavity is extremely large, are more brittle than those of the adult. It is possible that it may be placed in the cavities of the bones,—which would otherwise be so many vacant spaces,—to serve the general purposes of the fat, when it is required by the system. The other hypotheses, that have been entertained on the subject, are not deserving of notice.

5. Synovial Exhalation.

Within the articular capsules, and the bursæ mucosæ,—which have been described under the head of muscular motion,—a fluid is VOL. II.

27

« ZurückWeiter »