OF CELLS AND CELL-LIFE. 133 



a. Growth of the original cell, from its germ to its maturity ; involving 



the selection and appropriation of its materials. 



b. Multiplication, by the subdivision either of the original cell or of its 



nucleus. 



c. Chemical Transformation, exerted upon the pabulum of the cell, where- 



by new products may be generated in its interior. 



d. Vitalization of a portion of the pabulum, whereby it becomes endowed 



with vital properties of its own, so as even to originate cells de novo. 



e. Permanent Changes of Form, taking place in connection with acts of 



growth, and giving a peculiar character to the tissue. 



/. Temporary Changes of Form, applied to the generation of mechanical 

 force, and to the production of sensible motions. 



g. Production of Nerve-Force, which may affect all the preceding opera- 

 tions, and which is intimately related to Mental agency. 



The first five of these are manifested in those constructive operations, which are 

 common alike to the Plant and to the Animal, and which consist in the building- 

 up of the organized fabric. Of this organized fabric, on the other hand, the 

 exercise of the last two may be regarded as essentially destructive ; since they 

 involve an expenditure of that force which previously held together the compo- 

 nents of the tissues, whereby these components are given up to the disintegrat- 

 ing agency of the Chemical and Physical forces. But it is in the exercise of 

 Nervo-Muscular power that the Life of the Animal essentially consists; and the 

 constructive operations which take place in its fabric (as will be more fully 

 shown hereafter, CHAP. VI.), may be regarded as essentially destined to provide 

 its material and dynamical conditions. 



113. That these various phenomena are to be regarded as manifestations of 

 one and the same Vital Force, of which the several modifications of Organic 

 Structure that exhibit them are the respective instruments, may be argued, not 

 merely from the facts already urged, but also from the community of origin of 

 all the tissues and organs of each individual, in a single primordial cell. For, 

 like the humblest forms of Vegetable and Animal life which permanently con- 

 sist of separate and independent cells, the embryo of even the highest types of 

 each kingdom, in the earliest phase of its development, is but a single cell ; and 

 during the earlier period of its increase, we observe that it displays only that 

 most general manifestation of cell-force which consists in growth and multipli- 

 cation. The descendants of this parent-cell, however, soon begin to undergo a 

 variety of transformations, and to assume a diversity of characters ; and we ob- 

 serve, in fact, that a sort of "division of labor" takes place among them, each 

 group of cells being appropriated to some particular office, and discharging it 

 alone to the exclusion of the rest; as if, by this special direction of the vital 

 force, the cell which is its instrument is unfitted for any other kind of vital 

 agency. Of this relation of reciprocity between the several manifestations of 

 vital power, the following examples, among many others, may be cited. "Where 

 the whole energy of the cell is directed to multiplication, we do not observe 

 either chemical transformation, or change of form, or development into any other 

 tissue; nor do we find that either motor power or nerve-force is generated. Of 

 this we have already had an example in that early phase of embryonic life, in 

 which cell-multiplication takes place with extraordinary rapidity. In the for- 

 mation of new parts which make their appearance at a subsequent time, we find 

 that their foundation is laid in a mass of cells which rapidly multiply, up to a 

 certain point (like those of the embryonic mass), without any change of form or 

 character ; and that, when they have once begun to undergo development into 

 other kinds of tissue, they multiply no longer. So, again, in those cancerous 

 growths, whose rapid increase is one of their most important distinctive features, 



