16 PHYSICAL BASIS OF CIVILIZATION 



external parts, and which leaves the central sub- 

 stance almost unaffected. The longer the life of a 

 cell, the greater the opportunity for the concentra- 

 tion of like with like and dissociation from unlike 

 within it. The greater the mass and size of a cell, 

 the greater the freedom of the central substance 

 from the disturbances by extenal influences. See 

 Appendix, Note IV. 



Since the motions, however, of the substances 

 within the cell wall, by which the moving equilib- 

 rium of life is maintained, bring different portions of 

 its matter from moment to moment near to the inner 

 surface of the cell wall, therefore great caution must 

 be exercised, as it is very easy to apply the con- 

 clusions above reached too rigorously. 



But with due deductions made for this circum- 

 stance, there remains enough ground for the conclu- 

 sion that the external substance of a cell is far 

 more liable to modifications from environmental 

 influences than the central substance. In the lower 

 asexual forms of metaphyta and metazoa it is only 

 required to substitute the word "cells" for substances 

 or materials, and then the above arguments and con- 

 clusions apply equally to these. Thus the central 

 cells retain, to a very great extent, the original char- 

 acteristics of the substances and cells from which 

 they have been derived, — they become the carriers 

 of heredity. While the external cells are far more 

 subject to modification from environmental in- 

 fluences, and therefore become the means for varia- 



