Licence: Public Domain Mark
Credit: A text book of physiology / by William Rutherford. 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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![Cell Multiplication.—The simplest mode in which cells multiply is by fletnmation. We have already studied the process in the torula, and it is sufficient to add that in cells where the protoplasm is nucleated, the bud simply grows from the outer part of the protoplasm without any apparent participation of the nucleus in the process. But in the higher plants and animals gemmation is rare ; the common mode of cell multi- plication being/ssiOJi. As this process has been already described in the protaraoeba, amoeba, and ovum, it is sufficient to observe that as regai'ds the division of the protoplasm the process is similar in the presence or absence of the nucleus, but when the nucleus is present it divides before the protoplasm, and when the protoplast is enveloped in a periplast, the division of the former does not implicate the latter. In the ovum the fission of the protoplast occurs rapidly, and the peri- plasts secreted around some of the protoplasts have no connection with the original periplast—the Zona pellucida. But in the case of hyaline cartilage, where the cell-division usually takes place slowly, a new peri- plast is formed around each of the new protoplasts. The two layers of the periplast between the apposed surfaces of the protoplasts (Fig. 39) form a septum, which has been erroneously supposed to grow inwards from the original perijjlast. But it may happen that the cartilage protoplast proliferates rapidly, and a brood of young cells is enclosed within the original periplast, giving rise (Fig. 41) to an appearance not unlike that of the ovum during segmentation. The term endogenous is sometimes applied to this variety of the fissiparous mode. There are, therefore, only two essentially different modes in which the cell prolifer- ates—1, the gemmiparous ; 2, the fissi])arous—the endogenous mode being only a variety of the second of these. As long as Schwann's doctrine of the free formation of cells in a cyto- blastema outside other cells was believed, the term exogenous was employed to distinguish this mode. But as the production of cells in this manner is no longer generally credited, the term has become obsolete. CHAPTER V. THE GENERAL CHEMISTRY OF THE BODY. As it is impossible for the student to learn fully what is known of the chemistry of the body until the whole subject of mitrition has been studied in detail, it is proposed to give in this chapter merely such a general oidline of the subject as will enable him to comprehend the chemistry and nutrition of the simple tissues. THE FOOD AND THE EXCRETA. The nutrition of the organism requires the introduction of suitable quantities of (1) One or more proteids, e.g. albumin; (2) One or more](https://iiif.wellcomecollection.org/image/b21981747_0043.jp2/full/800%2C/0/default.jpg)
