Hand-book of physiology / by W. Morrant Baker and Vincent Dormer Harris.

  • William Morrant Baker
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: Hand-book of physiology / by W. Morrant Baker and Vincent Dormer Harris. Source: Wellcome Collection.

    42/910 (page 18)
    (cL) According to their functions, thej are called secreting, protective, sensitive, contractile, &c. (e.) According to their origin, they are named epiblastic, niesoblastic, and hypoblastic. Nearly all cells at some period of their existence possess imdeL As has been incidentally suggested the origin of a nucleus in a cell is the first trace of the differentiation of protoplasm. The existence of nuclei was first pointed out in the year 1833 by Eobert Brown, who observed them in vegetable cells. They are Fig. 12.—(a). Colourless Mood-corpuscle sJiowing intro-cellular networh of Heitzmann, and two nuclei with intra-nuclear network (Klein and Noble Smith). (b.) Coloured hlood-corpuscle of newt showintj intra-cellulor network of fibrils (Heitzmann). Also oval nucleus composed of limiting- membrane and fine intra-nuclear network of fibrils. X 800. (Klein and Noble Smith.) either small transparent vesicular bodies containing one or more smaller particles (nucleoli), or they are semi-solid masses of pro- toplasm always in the resting condition bounded by a well-defined envelope. In their relation to the life of the cell they are certainly hardly second in importance to the protoplasm itself, and thus Beale is fully justified in comprising both under the term u germinal matter.'' They exhibit their vitality by initiating, in the majority of cases, the process of division of the cell into two or more cells (fission) by first themselves dividing. Distinct observations have been made, showing that spontaneous changes of form may occur in nuclei as also in nucleoli. Histologists have long recognised nuclei by two important characters :— (i.) Their power of resisting the action of various acids and alkalies, particularly acetic acid, by which their outline is more clearly defined, and they are rendered more easily visible. This indicates some chemical difierence between the protoplasm of the cell and nuclei, as the former is destroyed by these reagents.