VARIATION IN GENERAL 9 



way sodium chlorid, for example, has always definite and well- 

 known properties not subject to variability. 



It is to be noted of course that the properties of the com- 

 pound NaCl are totally different from the properties of the ele- 

 ments that compose it, Na and Cl. They are nevertheless distinct 

 and invariable as well as new. This distinction between the varia- 

 bility of living matter and the constancy of non-living matter 

 should be borne in mind later on when discussing some of the 

 causes of variation. 



SECTION II VARIABILITY THE BASIS FOR 

 IMPROVEMENT 



Improvement is possible only where variability exists. The 

 compound NaCl being constant, it would be impossible to pro- 

 duce an improved variety of sodium chlorid, because the com- 

 pound is always the same and cannot be had with other than its 

 standard and invariable properties. Improvement in this com- 

 modity is limited, therefore, to its mechanical form and cannot 

 extend to its constitution. 



Living matter, upon the other hand, while possessed of defi- 

 nite properties, does not exhibit these properties always in the 

 same degree, and observation and experience have both shown 

 that profound changes may be made in either the form or the 

 constitution of both plants and animals by the simple method of 

 judicious combinations of desirable deviations. 



If there were no variability, and if living matter were as con- 

 stant in its properties as is non-living matter, then we should be 

 certain of what we already have, but no improvement would be 

 possible. As it is, with variability everywhere, living organisms 

 are both capable of improvement and liable to degeneration, for 

 both are the logical consequence of variability. Man must there- 

 fore work for what he possesses in the way of animals and 

 plants, and they will serve him well or ill according to his knowl- 

 edge and skill in dealing with their variations.. 



Accordingly he cannot know too much about the variations that 

 are likely to occur, their nature, their extent, and the causes 

 that control their appearance and determine their permanency. 



