466 CHEMICAL DISCOVERY AND INVENTION 



gates or clusters of molecules of various dimensions and possess- 

 ing a consistency which no solution could show, inasmuch as a 

 solution would possess viscosity and cohesion equal in every 

 direction. The amoeba if merely a drop of colloid solution 

 would, like a drop of any jelly, gradually melt away into the 

 surrounding water by the operation of ordinary liquid diffusion. 

 The amoeba has extensibility and retractility, and therefore cannot 

 be an ordinary solution. 



There is another point which seems to have escaped discussion 

 by biochemists. The skin which is formed on a warm colloid 

 solution, say of glue, is produced first because it is that part of 

 the liquid which is cooled most quickly, being exposed to the air. 

 The process of solidification gradually extends through the 

 entire mass, and the extent of the film is dependent on the size 

 of the vessel and the extension of the liquid. It is therefore 

 indefinite. But when a new cell is formed by partition or budding 

 a limit is set to the extension of the membrane. It continues to 

 grow till it reaches the average dimensions of the cells which 

 compose that particular kind of tissue. Consider the case of a 

 vegetable cell the wall of which is composed of cellulose. One 

 molecule after another of cellulose is generated within and is 

 added to pre-existent molecules and cemented to them by the 

 operation of an unknown cause, probably not ordinary chemical 

 attraction, or what is called cohesion, because of the limit which 

 is set to the process. The cell remains always small and micro- 

 scopic, only occasionally reaching such dimensions as to become 

 visible to the unaided eye. Ordinary chemical and physical 

 laws will not account for this phenomenon : no one can say as 

 yet what it is that makes molecule stick tenaciously to molecule, 

 forming so strong a continue u? membrane, and what it is that 

 puts a stop to the process when a sufficient extent of membrane 

 has been produced. Neither can anyone yet say why, in a mass 

 of cellular tissue in which cells all alike have been multiplying 

 side by side under the same conditions, some of these cells 

 suddenly take new forms and proceed to secrete new products, 

 such as colouring matters, not previously found in them. If 

 ordinary chemical and physical processes had the field to them- 

 selves, undisputed by that directive influence which is exercised 

 by the vital principle, whatever that is, there could be no orderly 

 arrangement in nature. Any living mass of cellular matter 

 provided with the necessary temperature, moisture, and pabu- 



