A manual of physiology : for the use of junior students of medicine / by Gerald F. Yeo.
- Date:
- 1884
Licence: Public Domain Mark
Credit: A manual of physiology : for the use of junior students of medicine / by Gerald F. Yeo. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![I. Peotoplasm is a colourless, pale, milky, semi-translucent sub- stance, more or less altered in appearance by various foreign matters which lie in it. These latter also give it a granular appearance, and when dead it commonly exhibits a linear marking or fine network. During life its consistence is nearly fluid, varying with the circum- stances in which it is placed, from that of a gum solution to a soft jelly. When living unmolested in its normal medium it seems to flow into various shapes, but this is a living action which does not prove it to be diflluent, for any attempt to investigate it by experiment causes a change in its consistence approaching to rigidity. As the full comprehension of the function of this substance lies at the root of the greater part of Physiology, the reader is referred for a detailed account of its properties to Chapter III. on Vital Phenomena, where it will be discussed at greater length. II. The Nucleus.— Most independent masses of protoplasm, and all highly organized cells, contain one or more nuclei in their sub- stance. The nucleus is in a greater or less degree sharply divided oft' from the surrounding] protoplasm. Its presence can generally be made much more conspicuous by treating the cell with various chemical re-agents, notably dilate acids and certain dyes. The nucleus is, in the former case, able to resist the action of dilute acetic acid for a much greater length of time than the remainder of the cell, so that it stands out clearly, while the rest becomes quite trans- parent. In the latter case, magenta (one of the aniline dyes) stains the nucleus sooner and deeper than the protoplasm. Although it has been accredited with special independent movements, it may safely be said that in comparison with the protoplasm it is not very contractile. Yet it appears to be intimately associated with the vital phenomena of the cell, and may be said to control or initiate the most important activities of the cell, namely, its division. The small size of the nucleus adds greatly to the difiiculty of investigating its functions, and much remains to be made out concerning both its structure and properties, although recently considerable progress has been made in this direction. III. The Cell Wall.—It has already been stated that the most active form-elements, such as the cells in the earliest stages in the life of an organism (embryonic cells), have no enclosing membrane or cell wall. But in the more advanced stages of cell life we And this second form of protoplasmic diflerentiation to be common enough. In animal cells the limiting membrane has never the same import- ance as the cell wall in vegetable tissues, where some of the principal textures may be traced to a du-ect modification of the cell](https://iiif.wellcomecollection.org/image/b21932943_0034.jp2/full/800%2C/0/default.jpg)
