Page:George Archdall Reid 1896 The present evolution of man.djvu/61

Rh mass; for instance, the mass of cells constituting a man owes its particular shape, the human shape, to certain definite inequalities which occur in the rates of multiplication in the lines of the cell-descendants of the germ whence the man is derived. Were there no inequalities in the rates of multiplication, did each line of cell-descendants multiply at the same rate, a solid, spherical mass of cells must result, whereas, owing to their unequal but definite rates of multiplication, the shape of the mass is irregular (i.e. not spherical), but nevertheless definite for man and every species of animal. An ox, therefore, differs in shape from a man mainly because the inequalities in the rates of multiplication in the various lines of the cell-descendants of the germ whence it is derived are different from the inequalities in the rates of multiplication in the lines of cells that spring from a human germ; but it resembles other oxen in shape, because the inequalities in the rates of cell-multiplication are much the same. Sometimes, however, though rarely, this or that cell-descendant of the germ reverts to the remote unicellular ancestral type, in so far that it does not multiply at a rate bearing a definite proportion to the rates of multiplication of its other co-descendants of the germ, but at a rate that has no definite proportion to them, and is only proportionate to its supply of nutriment and powers of assimilation. There then results the "morbid" condition which is known as a "tumour," in which the cell-descendants of a cell which has so reverted to the remote ancestral type form a more or less spherical mass which neither bears a definite proportion to the whole mass of the cell-community, nor performs definite functions beneficial to it, and is therefore an encumbrance or worse. But this tendency of cells to revert to the ancestral unicellular type, to multiply at a rate that is only proportionate to the supply of nutriment