180 THE CELL-THEORY 



(the nucleus) and then later round this a second layer (the 

 cell substance)" (p. 213). The outermost layer of the cell 

 usually thickens to form the membrane, but this membrane 

 formation does not always occur, and the membrane is 

 not present in all cells. The nucleus is formed in exactly 

 the same manner as the cell, and it might with much truth 

 itself be called a cell a cell of the first order, while ordinary 

 nucleated cells might be designated cells of the second order 

 (p. 212). In anucleate cells there is probably only a single 

 process of layer formation round an infinitely small nucleolus. 

 In almost all nucleate cells the nucleus is resorbed when the 

 cell reaches its full development, and it is larger and more 

 important the younger the cell is. 



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 pur- 

 posiveness 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 



