IV THE CELL AND THE ORGANISM 65 



and became active from within, with activities and func- 

 tions which reveal its inner character and nature, so to say. 

 It is a new structure in which energy becomes or is trans- 

 formed into a new form of activity, becomes functional, 

 becomes in some inexplicable way endowed with a power 

 of self-help and self-control, with special characters of 

 selectiveness and reproduction, which constitute a unique 

 departure in the universe. 



Let us summarise briefly some of the points that are known 

 of the structure and the functions of the cell; and as the 

 plant cell is simpler than the animal cell let us take that as 

 the 'type. It consists of chemically very complex substances 

 called in the aggregate protoplasm, which is the physico- 

 chemical basis of all forms of life. Comparatively little is 

 known of its composition or chemical structure. In the plant 

 cell (less so in the animal cell) it secretes a containing wall 

 or membrane for itself from which the cell derives its name. 

 Inside the wall the protoplasm appears as a jelly-like fluid 

 and consists principally of a small nucleus, which contains 

 certain chromatin bodies of a rich protein character, and of a 

 larger body of cytoplasm surrounding the nucleus and 

 reticular in structure, that is to say, consisting of a network 

 of spaces which contain various cell-saps and solutions and 

 even minute particles of crystals and other inorganic bodies. 

 The whole constitutes a colloidal system, as we saw in the 

 last chapter. The cell walls are semi-permeable, admitting 

 of the osmosis through them of certain substances and not 

 of others, so that suitable food and other substances can be 

 passed through the cell walls from one cell to another. There 

 is a constant circulation and agitation of the cell fluid, which 

 gives it the appearance of a stream, and is much more than 

 the usual promiscuous Brownian movement in inorganic 

 colloidal mixtures. The movement of protoplasm, whether 

 it is Brownian or something different, has much more of the 

 character of definite specific direction; and this is probably 

 only an expression of that selectiveness and directiveness 

 which are inherent and universal characteristics of all life- 

 forms. Although little is definitely known of the details of 



