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At the lower or vegetal pole of the ovum a crown of eight large entodermic cells remains for a long time unchanged, while the other cells divide, owing to the formation of a series of horizontal circles, into an increasing number of crowns of sixteen cells each. This layer is the blastoderm, the simple epithelium from the cells of which all the tissues of the body proceed.
Any ulcer may get into a weak state from receiving a blood supply which is defective either in quantity or in quality. The granulations are small and smooth, and of a pale yellow or grey colour, the discharge is small in amount, and consists of thin serum and a few pus cells, and as this dries on the edges it forms scabs which interfere with the growth of epithelium.
In some cases, healing goes on more rapidly under a dressing of weak boracic ointment (one-quarter the strength of the pharmacopœial preparation). The growth of epithelium may be stimulated by a 6 to 8
The chronic and intractable character of the ulcer is due to interference with the trophic nerve-supply of the parts, and to the fact that the epithelium of the skin grows in and lines the track leading down to the deepest part of the ulcer and so prevents closure.
A highly magnified view of a peptic or gastric gland, which is represented as giving off branches. It shows the columnar epithelium of the surface dipping down into the duct D of the gland, from which two tubes branch off.
As we have seen, bacteria exist everywhere, mixed with the dust that interferes with the transparency of the air and covers all objects; and they are likewise found in water. Under normal conditions, our body is closed to these organisms through the epidermis and epithelium, and, as has been shown by Mr. Pasteur, no bacteria are found in the blood and tissues of living animals.
It is made up of two layers—a thick underlayer which contains blood vessels, nerves, and glands, and a thin surface layer, called the epithelium. The epithelium, like the cuticle, is without blood vessels, nerves, or glands. A middle coat, which is muscular and which forms a continuous layer throughout the canal, except at the mouth.
In the embryo, the cortex is derived from the same patch that gives rise to the sex organs, the ovaries in the female, and the testes in the male, described as the germinal epithelium. How intimately the two sets of glands are connected is neatly pointed by this fact of a common ancestor. All vertebrates possess adrenal glands.
The capillaries are the minute, hair-like tubes, with very thin walls, which form the connection between the ending of the finest arteries and the beginning of the smallest veins. They are distributed through every tissue of the body, except the epidermis and its products, the epithelium, the cartilages, and the substance of the teeth.
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