192 THEORY OF THE CELLS. 



tially similar laws j and, therefore, that these processes must, 

 in every instance, be produced by the same powers. Now, if we 

 find that some of these elementary parts, not differing from 

 the others, are capable of separating themselves from the 

 organism, and pursuing an independent growth, we may thence 

 conclude that each of the other elementary parts, each cell, 

 is already possessed of power to take up fresh molecules and 

 grow ; and that, therefore, every elementary part possesses a 

 power of its own, an independent life, by means of which it 

 would be enabled to develop itself independently, if the relations 

 which it bore to external parts were but similar to those in 

 which it stands in the organism. The ova of animals afford 

 us examples of such independent cells, growing apart from the 

 organism. It may, indeed, be said of the ova of higher animals, 

 that after impregnation the ovum is essentially different from 

 the other cells of the organism ; that by impregnation there 

 is a something conveyed to the ovum, which is more to it than 

 an external condition for vitality, more than nutrient matter ; 

 and that it might thereby have first received its peculiar 

 vitality, and therefore that nothing can be inferred from it with 

 respect to the other cells. But this fails in application to those 

 classes which consist only of female individuals, as well as with 

 the spores of the lower plants ; and, besides, in the inferior 

 plants any given cell may be separated from the plant, and 

 then grow alone. So that here are whole plants consisting 

 of cells, which can be positively proved to have independent 

 vitality. Now, as all cells grow according to the same laws, 

 and consequently the cause of growth cannot in one case lie 

 in the cell, and in another in the whole organism ; and since 

 it may be further proved that some cells, which do not differ 

 from the rest in their mode of growth, are developed indepen- 

 dently, we must ascribe to all cells an independent vitality, that 

 is, such combinations of molecules as occur in any single cell, 

 are capable of setting free the power by which it is enabled 

 to take up fresh molecules. The cause of nutrition and 

 growth resides not in the organism as a whole, but in the 

 separate elementary parts — the cells. The failure of growth 

 in the case of any particular cell, when separated from an 

 organized body, is as slight an objection to this theory, as it 

 is an objection against the independent vitality of a bee, that 



