Schwann, in 1836, showed that the important thing about a “cell” is not the box or cell-wall so much as the viscid contents and the nucleus. But the name “cell” was (strangely enough) retained for the contents, even when the box-like chamber was absent—much as we speak of “a bottle of wine,” meaning the contents of the bottle, and not the glass vessel holding it. It was shown that the box-like case or cell-wall (the original “cell” of Hook) is actually formed by the living nucleated plasm or viscid matter within it, just as a snail forms its shell, by the separation or “secretion” of a dead, firm, chemical deposit on its living surface. Schwann showed that all—not merely special exceptional instances, but all—the tissues of plants and of animals are built up by nucleated cells, the cell-wall being often not hard and box-like, but soft, gelatinous, irregular in shape, and sometimes very thin, sometimes very thick. Every living cell is thus surrounded by the chemical products of its own activity, or may deposit those products within itself as in the goblet-cell and the fat-cell seen in Fig. 40, C and D, and these products differ in different tissues. The cells of a tissue, using the word to mean the soft nucleated particles or corpuscles of protoplasm or “cell-substance,” must be regarded as the microscopic living “weavers” or makers of the tissue. The cells in one tissue may form a honeycomb of boxes; in another a jelly-like mass or a fibrous network, with the cell-substance scattered as nucleated particles in it (Fig. 39). Or the cells may be elongated and contractile (Fig. 37, E, F). They may be more or less fused with one another, as in flesh or muscular fibre; but we can always recognise the presence of the individual cells under the microscope by their distinct and separate “nuclei.” [Illustration: FIG. 40.—Three kinds of cells, magnified a thousand times linear. A, a row of cilia-bearing cells. B, a single detached ciliated cell: observe the nucleus in each cell. C, a goblet-cell, from a mucous surface, producing _c_, a slimy secretion; _d_, the wall of the cell; _b_, the nucleus; _a_, the protoplasm in which the secretion _c_ was accumulated until it burst out at the free end of the cell. D, a fat-cell; _a_, the nucleus surrounded by protoplasm; _e_, the thin layer of protoplasm enveloping the great oil drop _f_, which has formed within it.]