Page:Popular Science Monthly Volume 71.djvu/106

100 two divided cells are smaller than the mother cell and have smaller nuclei. They will, however, presently grow up and attain the size of their parent.

Every cell is a unit both anatomically and physiologically. It has a certain individuality of its own. In many cases cells are found to be isolated or separated completely from one another. But, on the other hand, we also find numerous instances in which the living substance of one cell is directly continuous with that of another. When the cells are thus related, we speak of the union of cells as syncytium. Of this I offer you an illustration in the second picture upon the screen which represents the embryonic connective tissue of man. In this you can see the prolongations of the protoplasm of a single cell body uniting with the similar prolongations from other cell bodies, the cells themselves thus forming, as it were, a continuous network with broad meshes between the connecting threads of protoplasm. The spaces or meshes are, however, not entirely vacant, but contain fine lines which correspond to the existence of fibrils, which are characteristic of connective tissue and at the stage of development represented in this picture, are beginning to appear. It is fibrils of this sort which we find as the main elements in the constitution of sinews and tendons, as, for instance, the tendon of Achilles, at the heel. In a very young body we find there are but few fibrils; in the adult body an immense number.

There is, in fact, as you probably all know, a constant growth of cells; and this growth implies also, naturally, their multiplication. There has been in each of us an immense number of successive cell