Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/117

Rh brilliant confirmation of the correctness of the view, that the fibres of the crystalline lens are really cells, however much they may deviate from the fundamental type of the cellular form.

There is no longer, therefore, any more difficulty in explaining the process of nutrition in the lens, than there is that of plants. The cells grow by their own independent force, and blood-vessels are unnecessary, as the nutrient fluid can be conducted from one cell into another. A morbid change of the cell-vitality, rendering the cell-contents opaque, is also possible.

The structures included in this class, notwithstanding the strong general resemblance which they bear to each other, have furnished us with far more varied modifications of the cellular form than the previous class exhibited; indeed, these so-called unorganized tissues have already prefigured the type of all the changes by which the organized tissues are developed from simple cells. Here, also, the fundamental form of the cells is that of a sphere, which, in consequence of their close contact, passes over, from mechanical causes, into a polyhedral figure. Two different modifications of this fundamental form occur, which cannot be explained mechanically; they are the flattening of the cells on two opposite sides to form tables, and their elongation in two directions into cylinders or fibres. We have already seen an instance of flattening of the cells in the blood-corpuscles of the previous class. It is not only more strongly marked here in the tabular epithelium, where the cell-cavity is quite obliterated, but a modification even of this form is presented to us in the elongation of these tables on two sides into flat stripes, as seen in the epithelium of the internal coat of veins for example, and still more distinctly in the cortical substance of the shaft of the raven’s feather. The epithelium of many of the mucous membranes, that of the intestine for instance, which Henle describes as consisting of little palisade-like cylinders placed close to one another, furnishes us with a rudimentary form of the elongation of cells into cylinders and fibres. Sometimes these little cylinders become acuminated at their lower extremity, or they may diminish throughout their entire length from above downwards, and thus become small cones.