Fig. 427.
1. White fibrous tissue lining the interior of the egg shell, with the calcium carbonate removed by immersion in hydrochloric acid; 2. White fibrous tissue, from the sclerotic coat of the eye.
White fibrous tissue presents silver-lustre bundles, running for the most part in parallel directions through and over the muscles and tendons. For examination under the microscope, obtain a fragment of fresh meat cut in the longitudinal direction; place it in water, and tease it out with needles as directed in a former chapter. The smallest fragment will suffice for examination under a quarter or one-sixth inch objective. These filaments are exceedingly minute, measuring 1⁄3000th to 1⁄2500th of an inch in diameter, and do not interlace through the bundles, although they intersect each other occasionally. Transverse sections may be made by drying a piece of tendon until it becomes sufficiently firm to cut with a razor or microtome, and mounted as a permanent specimen. From the cut ends of the fibres small dark points will be seen, especially in the denser structure of the tendons; these are termed “connective tissue corpuscles.”
Yellow elastic fibrous tissue is remarkable in contradistinction to the white for its elasticity and capability of extension. It is found on the coats of blood-vessels, between the vertebral arches, and in quadrupeds it forms a strong elastic band, extending from the occiput, throughout the spines of the vertebra, and enabling the animal to support the head in the pendent position, without muscular exertion. These fibres can only be separated from each other with difficulty, and their elasticity is shown by a tendency to curl up. These yellow fibres are somewhat coarser than the white, and they remain unaffected by acetic acid of the ordinary strength. Elastic tissue is a constituent of the skin, mucous, and serous membranes, and of the areolar or cellular tissue.
In order to microscopically examine this structure, take a small portion of the strong ligament of the neck of the ox, place it as before in water, and tease it out with needles; place a fragment on a glass slip, cover with a thin cover-glass, and submit it to a high magnifying power. Transverse sections made as directed in the case of white tissue will be seen to be hexagonal in form.
Adipose Tissue.—Fat is found in many situations in the animal body, and on examination is seen to consist entirely of vesicles, distributed through a delicate membrane of connective tissue, shown in [Plate XIX]., Nos. 4 and 5. On pressure, the circular or oval form of the cells becomes polyhedral; occasionally the fatty acids in the interior of the vesicles crystallise, and give rise to a star-like appearance. For the examination of adipose tissue, take a portion of the mesentery of any small animal—a mouse, or rat.
Retiform Tissue.—Adenoid, or retiform tissue, consists of a delicate network of connective tissue corpuscles, joining their branches together. This forms the stroma or framework of lymphoid tissue. It is found in connection with all the lymphatic glands, spleen, &c. [Plate XIX]., No. 3, a b, shows small sections of a lymphatic, together with capillary vessels.
Muscular Fibre.—There are two varieties of muscular fibre in the body—i.e., striated, and non-striated. The striated is formed in muscles attached to bony structures, as those of the arm and leg, and in some of the soft structures, as the tongue, palate, œsophagus, in short, all muscles under the control of the will. Striped muscle is of a dull red colour and marked with peculiar longitudinal furrows on its surface. Voluntary muscle consists of:—1, a connective tissue sheath; 2, fasciculi; 3, fibres and sarcolemma; 4, discs, fibrilla and sarcous elements. These are shown in connection with other tissues in [Plate XIX]., Nos. 11 and 12, and also in [Fig. 428] (1, 2, 3).
