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Epithelium is only reproduced from pre-existing epithelium, and, as a rule, from one of a similar type, although metaplastic transformation of cells of one kind of epithelium into another kind can take place.
Cancer may arise on any surface covered by epithelium or in any of the secreting glands of the body, but it is much more common in some situations than in others. It is frequently met with, for example, in the skin, in the stomach and large intestine, in the breast, the uterus, and the external genitals; less frequently in the gall-bladder, larynx, thyreoid, prostate, and urinary bladder.
"It is therefore evident that the phenomena belong not to the function of menstruation, but to a general law of vital energy." Definition of Menstruation. Menstruation may, then, be defined as the periodic discharge of blood from the uterus, accompanied by the shedding of the epithelium of the body, as well as that of the uterine glands near their orifices.
The edges are inflamed, irregular, and ragged, showing no sign of growing epithelium on the contrary, the sore may be actually increasing in area by the breaking-down of the tissues at its margins. The surrounding parts are hot, red, swollen, and œdematous; and there is pain and tenderness both in the sore itself and in the parts around.
As the main local obstacle to healing is the down-growth of epithelium along the sides of the ulcer, this must be removed by the knife or sharp spoon. The base also should be excised, and any bone which may have become involved should be gouged away, so as to leave a healthy and vascular surface.
The epithelial structures may be divided, as to their functions, into two main divisions. One is chiefly protective in character. Thus the layers of epithelium which form the superficial layer of the skin have little beyond such an office to discharge.
The columnar epithelium consists of pear-shaped or elongated cells, frequently as a single layer of cells on the surface of a mucous membrane, as on the lining of the stomach and intestines, and the free surface of the windpipe and large air-tubes. The glandular or spheroidal epithelium is composed of round cells or such as become angular by mutual pressure.
The edges, noting particularly whether or not the marginal epithelium is attempting to grow over the surface; also their shape, regularity, thickness, and whether undermined or overlapping, everted or depressed. The surrounding tissues, as to whether they are congested, œdematous, inflamed, indurated, or otherwise. Whether or not there is pain or tenderness in the raw surface or its surroundings.
The histology of ainhum shows it to be a direct ingrowth of epithelium, with a corresponding depression of surface due to a rapid hyperplasia that pushes down and strangles the papillae, thus cutting off the blood supply from the epithelial cells, causing them to undergo a horny change. The disease is not usually symmetric, as formerly stated, nor is it simultaneous in different toes.
However this obstruction may be brought about, whether by thickening of the iris root during dilatation of the pupil, pushing forward of the iris root by the larger ciliary processes of age, or the enlarged crystalline lens pressing on the ciliary processes; or by inflammatory adhesion of the iris to the filtration area; ballooning of the iris, or its displacement by traumatic cataract; or adhesion to the cornea after perforating ulcer in the secondary glaucomas; or whether the obstruction is due to the accumulation of experimental precipitates, as shown by Schreiber and Wengler, or possibly of pigment granules into Fontana's space; or a process of sclerosis closing the spaces by contraction of new-formed connective tissue, or the covering over with proliferating implanted epithelium following injury opening the anterior chamber; glaucoma follows impairment of this drainage space, and lessened outflow through it.
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