Fig. 3.
Fig. 3. Arrangement of fibres of the cellular tissue magnified one hundred and thirty diameters.
28. What is a tissue? 29. What is said respecting the structure and composition of the various organs? Name the primary membranes. 30. Describe the cellular tissue. How are the cells imbedded in certain tissues? Give observation 1st, relative to the cellular tissue.
Observations. 1st. When this fluid becomes too great in quantity, in consequence of disease, the patient labors under general dropsy. The swelling of the feet when standing, and their return to a proper shape during the night, so often noticed in feeble persons, furnish a striking proof both of the 20 existence and peculiarity of this tissue, which allows the fluid to flow from cell to cell, until it settles in the lower extremities.
2d. The free communication between the cells is still more remarkable in regard to air. Sometimes, when an accidental opening has been made from the air-cells of the lungs into the contiguous cellular tissue, the air in respiration has penetrated every part until the whole body is so inflated as to occasion suffocation. Butchers often avail themselves of the knowledge of this fact, and inflate their meat to give it a fat appearance.
31. “Although this tissue enters into the composition of all organs, it never loses its own structure, nor participates in the functions of the organ of which it forms a part. Though present in the nerves, it does not share in their sensibility; and though it accompanies every muscle and every muscular fibre, it does not partake of the irritability which belongs to these organs.”
32. Several varieties of tissue are formed from the cellular; as, the Se´rous, Der´moid, Fi´brous, and several others.
33. The SEROUS TISSUE lines all the closed, or sac-like cavities of the body; as, the chest, joints, and abdomen. It not only lines these cavities, but is reflected, and invests the organs contained in them. The liver and the lungs are thus invested. This membrane is of a whitish color, and smooth on its free surfaces. These surfaces are kept moist, and prevented from adhering by a se´rous fluid, which is separated from the blood. The use of this membrane is to separate organs and also to facilitate the movement of one part upon another, by means of its moist, polished surfaces.