ADIPOSE T I SS U E.—( Lat. Tela adiposa Fr. tissu adipeux, tissu graisseux, Germ. das Fat, Ital. adipe.
Many of the old anatomists, as Mondini, Berenger, Vesalius, and Spigelius, represent the fat (adeps vel pinguedo) of the animal body as entirely distinct from the membrana carnosa, or cellular membrane. The separate existence of a proper adipose membrane, however, si tuate between the skin and the filamentous tissue, or membrana CaillOSa, was first taught by Malpighi, then distinctly maintained by De Bergen and Morgagni, and finally demon strated by William Hunter. Collins, James Neill, and other anatomists adopted the views of Malpighi, and Haller was disposed latterly to imitate De Bergen and Morgagni, in assigning to the fat of the animal body a situation dis tinct from that of the cellular membrane. And in this country the independent existence of the adipose membrane was recognized by Bromfield, John Hunter, and others.
It was still, however, confounded with that of the filamentous tissue under the general name of cellular membrane, adipose mem brane, and cellular fat, by Winslow, Dionis, Portal, Sabatier, Bichat, and Meckel, and described as a variety or modification of the cellular membrane; and Blumenbach considers it as a secretion into that membrane. Its dis tinct existence from the cellular membrane was finally admitted by M. Beclard, and its anato mical and physiological relations as well as its chemical properties have been since minutely investigated by M. Raspail.
According to the dissections of De Bergen and Morgagni, the demonstrations of Hunter, and the observations of M. Beclard, the struc ture of the adipose membrane consists of rounded packets or parcels (pelotons) separated from each other by furrows of various depth, of a figure irregularly ovoidal, or spheroidal, va rying in diameter from a line to half an inch, according to the degree of obesity in the part submitted to examination. Each packet is composed of small spheroidal particles which may be easily separated by dissection, and which are said to consist of an assemblage of vesicular bags still more 'Minute, aggregated together by very delicate filamentous tissue. These were originally described by Malpighi under the name of membranous sacculi, and by Morgagni under that of sacculi pinguedi nosi.
The appearance of these ultimate vesicular pouches is minutely described by Wolff in the subcutaneous fat, and by Clopton Havers* and the first Monro in the marrow of bones, in which the two last authors compare them to strings of minute pearls. If the fat with which these vesicles are generally distended should disappear, as happens in dropsy, consumption, chronic dysentery, and other wasting diseases, the vesicular sacs collapse, their cavity is obli terated, and they are confounded with the con tiguous cellular tissue without leaving any trace of their existence.
Hunter, however, asserts that in such cir cumstances the cellular tissue differs from the tissue of adipose vesicles in containing no similar cavities, remarks that the latter is much more fleshy and ligamentous than the fila mentous tissue, and contends that though the adipose vesicles are empty and collapsed, they still exist. When the skin is dissected from the adipose membrane, it is always possible to distinguish the latter from the filamentous tissue, even if it contain no fat, by the tough ness of its fibres and the coarseness of the web which they make.
The distinguishing characters between the cellular or filamentous and the adipose tissue may be stated in the following manner. First, the vesicles of the adipose membrane are closed all round, and, unlike the cellular tissue, they cannot be generally penetrated by fluids which are made to enter them. If the temperature of a portion of adipose membrane be raised by means of warm water to the liquefying point of the contents, they will remain un moved so long as the structure of the vesicles is not injured by the heat. If again an adi pose packet be exposed to a solar heat of 104° Fahrenheit, though the fat be completely lique fied, not a drop will escape until the vesicles are divided or otherwise opened, when it ap pears in abundance. The adipose matter, therefore, though fluid or semifluid in the living body, does not, like dropsical infiltra tion, obey the impulse of gravity. Secondly, the adipose vesicles do not form, like cellular tissue, a continuous whole, but are simply in mutual contiguity. This arrangement is de monstrated by actual inspection, but becomes more conspicuous in the case of dropsical effu sions, when the filamentous tissue interposed between the adipose molecules is completely infiltrated while the latter are entirely unaf fected. Thirdly, the anatomical situation of the adipose tissue is different from that of the filamentous tissue. The former is found, 1st, in a considerable layer extended immediately beneath the skin ; 2dly, in the trunk and ex tremities round the large vessels and nerves ; 3dly, between the serous and muscular tissues of the heart ; 4thly, between the peritoneal folds which form the omentum and mesentery ; 5thly, round each kidney; and, Gaily, in cer tain folds of the synovial membranes without the articular capsules.