Page:Popular Science Monthly Volume 71.djvu/366

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POPULAR SCIENCE MONTHLY

other condition of a cell of the skin of the salamander in which the nucleus presents a slightly different appearance. Here also we have quite a body of protoplasm about the nucleus. Every cell consists of these two essential and fundamental parts, the nucleus and the protoplasm. Now the conclusion to which I shall gradually bring you by

PSM V71 D366 Cells from the oral epithelium of the salamander.png

Fig. 39. Cells from the Mouth (Oral) Epithelium of the Salamander.

the facts to be laid before you this evening is that the increase of the protoplasm is the thing which is to be regarded as the explanation of senescence. Though protoplasm is the physical basis of life, though it is the actual living substance of the body, its undue increase beyond the growth of the nucleus changes the proportions of the two. and that change of proportion seems to cause an alteration in the conditions of