ABSORPTION AND MOVEMENT OF WATER 161 



its exosmosis in another part. Similarly in the filamentous 

 alga, the accumulation of sugar in its cells bounded on all 

 sides by membranes permeable by water is conceivable only 

 on the hypothesis, strengthened by analogy ( p. 107 ) , that 

 the living protoplasm in some way interferes, either physi- 

 cally or chemically, with the exosmosis of the sugar. 



To summarize the results of the discussions in this chapter 

 we may say that diffusion and osmosis underlie the pro- 

 cesses of absorption and transfer of food-materials and of 

 foods, but that the movements of these gases and solutions, 

 and of the separate substances in the solutions, are con- 

 trolled in direction, rate, and amount by the living proto- 

 plasm. Its needs, and the amount and kind of work it 

 does, change or establish physical conditions and set in 

 operation physical and chemical laws. 



