The cell was for Schwann not a morphological concept at all, but a physiological; the cell was a dynamical, not a statical unit. Cell-formation was the process at the back of all production of life, and cells were the centres of all vital activity. Each cell was itself an organism, and its life and activities were to some extent independent of the lives and activities of all the other cells. The multicellular organism was a colony of unicellular organisms, and its life was a sum of the lives of its constituent elements. This "theory of the organism," which holds so important a place in biology even at the present day, is developed by Schwann in the concluding pages of his book. He begins by contrasting the teleological with the materialistic conception of living things. In the teleological view, a special force works in the living organism, guiding and directing its activities towards a purposeful end. According to the materialistic view there are no other forces at work in the living organism than those which act in the inorganic realm, or at least there are none but forces at one with these in their blindness and necessity. True, the purposiveness of living processes cannot be denied; but its ground lies, according to this view, not in a vital force which guides and rules the individual life, but in the original creation and collocation of matter according to a rational plan. The purposiveness of life is part of the purposiveness of the universe; just as the stars circle for ever in harmoniously adjusted paths, so do the processes of life work together towards a common end. Both are the inevitable result of the original distribution of matter in the primitive chaos, a distribution fixed by a rational and foreknowing Being (p. 222). Which of the two conceptions is to be adopted in biology? Teleological explanations have long been banished from the physical sciences, and in biology they are only a last resort when physical explanations have proved incomplete (p. 223). And if the ground of the purposiveness of living Nature is the same as the ground of the purposiveness of the universe, is it not reasonable to suppose that explanations which have proved satisfactory for inorganic things will in time with sufficient knowledge prove adequate also for organic things?