. General physiology; an outline of the science of life. 68 GENERAL PHYSIOLOGY characterises all other cells. There are also among animals varieties of cells that show quite the same quantitative relation of the two substances to each other; an example of such is afforded by the sperm-cells, or spermatozoa, which consist of a large quantity oi nuclear substance and a very small quantity of protoplasm. Thus, from the present state of our knowledge, it appears that among the organisms now living upon the earth there are no cells in which a separation of two different substances is not present, b
. General physiology; an outline of the science of life. 68 GENERAL PHYSIOLOGY characterises all other cells. There are also among animals varieties of cells that show quite the same quantitative relation of the two substances to each other; an example of such is afforded by the sperm-cells, or spermatozoa, which consist of a large quantity oi nuclear substance and a very small quantity of protoplasm. Thus, from the present state of our knowledge, it appears that among the organisms now living upon the earth there are no cells in which a separation of two different substances is not present, but that every cell possesses a nucleus in addition to the proto- plasm. It is, of course, another question whether during the evolution of living substance upon the earth organisms may not have existed at some earlier time, in which the whole body consisted of a single homogeneous substance, and no separation into different substances had yet taken place. If such organisms ever. PiQ. 9,—structure of various Bacteria. (After BUtsehli.) a, Bacterium lineola, normal and under- going division. 6, Spirillum undula, c, Bactm-ium from stagnant water. existed, they could be ranked in comparison with real cells as cytodes, as Haeckel terms non-nucleated elementary organisms. Notwith- standing them, it must be granted that there belongs to the conception of the cell at present, not only a single homogeneous mass, the protoplasm, but also a substance differing from it, the nuclear substance. Accordingly, Max Schultze's morphological definition would be widened as follows : The cell is a hit of protoplasm containing a distinct nucleus. If the protoplasm be examined with strong magnifying powers, in many cells other distinct constituents besides the nucleus are found embedded in the protoplasmic ground-substance. In many cells oil-droplets occur, in others pigment-granules, in plant-cells starch-grains, etc.; but all these bodies do not occur in every kind of cell: they are special, not g
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