A text-book of human physiology / by Dr. Robert Tigerstedt ... tr. from the 3d German ed. and edited by John R. Murlin ... with an introduction to the English ed., by Professor Graham Lusk.

Robert Tigerstedt

Date:: 1906

Credit: A text-book of human physiology / by Dr. Robert Tigerstedt ... tr. from the 3d German ed. and edited by John R. Murlin ... with an introduction to the English ed., by Professor Graham Lusk. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

58/794 page 22

$the body is deposited. Eggs likewise contain an abundant su])|)ly of proteid, lecithin and fat which are to serve as nourishment for tiie developing embryo. Oiher inclosures which occur in greater or less abinulaiK'(^' in animal cells, are: fat droplets in the cells of the maniniary glands and of the intestinal mucosa during absorption; pigment g:ranules in the pigment cells of the skin and of the choroid coat in the eye; glycogen granules in the liver cells, etc. In the naked cells which are able to take up solid particles from the surrounding medium we observe often small Algae, Bacteria, Infusoria and the like (Figs. 19, 20, 21 and 22), which serve as nourishment for the cell, and, after digestion is completed, indigestible shells, skeletons, envelopes, etc. Again small cavities filled with fluid (vacuoles) are present in the protoplasm of certain animal cells. Among these are to be mentioned especially the so-called contractile vacuoles, i. e., drops of fluid which are pressed out of the protoplasm by the contraction of a surrounding sheath, only to be re-collected from the protoplasm in the same place again when the contraction ceases (Figs. 21, 24, 2S). Finally, there are found within the protoplasm of animal cells certain plant cells, Algje. which do not serve their host as nutritive material, but merely live in company with it (symbiosis). They are of the greatest importance to the life of the animal cell in which they occur, since through the activity of their chlorophyll bodies, they supply it with the necessary oxygen, thereby rendering it independent of the oxygen contained in the surrounding medium. We have the most beautiful instance of symbiosis in a lichen, which is nothing more than an aggregate individual consisting of a fungus and an alga. Reference must be made to works on cytology and histology for a discussion of the ultimate structure of the protoplasm, nucleus and centrosome, as well as for the changes in these accompanying cell division. § 2. THE VITAL PHENOMENA OF CELLS A. INTRODUCTORY SURVEY The vital activity of all cells, both plant and animal, consists of two oppo- site processes, assimilation and dissimilation. We include under assimilation all the synthetic processes, of whatever kind, going on in the cell or under its influence; under dissimilation all the disintegration processes going on in the cell or under its influence. A. Assimilation is of two kinds, namely growth of protoplasm, i. e., for- mation of living substance, and syntheses of new substances not living. Our knowledge of the growth of protoplasm is still very meager. We can observe how the cell increases in size, and how it multiplies after it has reached a certain size, hut the inner mechanism of these processes is still quite obscure. Somewhat more satisfactory is our knowledge of the syntheses of organic nonliving substances accomplished by cells. In fact the synthesis which is quite the most impo-tant of all, namely, the formation of starch in the green parts of plants, is known with tolerable exactness, and may be described briefly as follows: There always occur in the neighborhood of the nucleus of plant cells small, colorless, highly refractive bodies, for the most part oval or elliptical in form,' which are called trophohlaats and which arise always, like the nucleus and the$