Animal physiology / by John G. M'Kendrick.

  • John Gray McKendrick
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: Animal physiology / by John G. M'Kendrick. Source: Wellcome Collection.

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    formation may be seen in cartilage and in cancer cells ; it is very doubtful if there are any true examples of exogenous formation—some authors denying its occurrence; fissiparous division may be noticed in the cells of the embryo, and sometimes in colourless corpuscles and pus cells ; and gemmiferous formation or budding has been observed in the development of blood-corpuscles, and may be readily studied in the yeast plant {Torula cerevisice)^ when a drop of yeast is examined from time to time under the microscope. 34. Varieties of Cells.—Cells may be divided into : (i) normal isolated cells, floating in a fluid, such as lymph, chyle, and blood-corpuscles ; (2) cells with a small amount of intercellular matter, such as epithelial cells ; (3) cells imbedded in, and intimately connected with, other tissues, such as fat cells, pigment cells, and nerve cells ; (4) cells on free membranes which secrete various fluids—secreting or gland cells ; (5) cells which, during different periods in their earlier stage of development, present all the characters and functions of cells, but the tendency of which is to be trans- formed, or so arranged as to constitute a tissue—cells of transition—such as cartilage, colloid, connective tissue, and embryonic cells; and (6) cells found only in morbid conditions of the tissues, such as pus cells, cancer cells, and tubercle corpuscles. Several of the different varieties of cells will be described when we treat of the fluid or tissue in which they are found, but there are certain kinds which must now be noted. Epithelium and Endothelium. 35, General Description of Epithelium.—This is a tissue composed of cells in layers of greater or less thickness, which (i) covers the external and internal surfaces of the body, (2) lines the canals of exit, and (3) clothes numerous closed cavities, such as that between the wall of the chest and the lungs, termed the pleura. The cells found on free surfaces and in ducts are called epithelial cells, while those which Mne the shut cavities have recently been-
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