No. 448.] 



HEREDITY AXD ENVIRONMENT. 



289 



of pure water, but the specific gravity of the water itself and 

 of the solute itself are the same as they have always been, 

 the specific gravity of the solution depending only upon these 



With its physical and chemical properties unchanged, as an 

 essential constituent of all living organisms and the medium in 

 which necessarily the food materials and foods enter and move 

 about and are chemically changed in the cell, water has exerted 

 upon living things an influence as powerful and as persistent as 

 have been its relations to the physical and chemical conditions 

 and processes of lifeless substances since the beginning. Water 

 can be eliminated neither outright nor by substitution from 

 experiments with living organisms nor, for that matter, can it be 

 eliminated from the majority of experiments with lifeless sub- 

 stances. It is a substance of universal occurrence, of uniform 

 properties, of uniform action. It is truly one of the unchanging 

 factors of the environment, to which living organisms necessarily 

 react, for their composition, structure, nutrition, and activities 

 depend upon it. 



We come now to consider the effect of gravitation. The 

 force of gravity acts upon every particle of ponderable matter 

 on the earth as a direct pull toward the center of the earth. 

 This pull is equal, at the surface of the earth, to 32.2 foot 

 seconds-, e. a body at the surface of the earth would fall in 

 a vacuum at a rate increasing 32.2 feet a second per second. 

 The force of gravity, operating upon every particle of i)on(lerable 

 matter, constantly exerts upon it this uniform force. 1 he lorce 

 increases or decreases inversely as the squares of the distaiucs. 

 But, as Newton showed, the force of gravity is not merely the 

 attraction between the earth as a whole and other jM.nderable 

 matters, but every portion of matter attracts every other 

 with a force proportional to the product of their masses (h\i( ec 

 hy the square of their distances apart.' I he sum of the atti ac- 

 tions toward the center of the earth equals thi amount i)revi- 

 •Hisly mentioned, 32.2 foot seconds-, and this sum we nia\ or 

 the moment speak of as gravity without necessarily taking its 

 components into account. 



