188 THE INDUCTIONS OF BIOLOGY. 



to perform certain difficult feats ; but certain more difficult 

 feats, no additional practice enables him to perform. Years of 

 discipline give tbe singer a particular loudness and range of 

 voice, beyond which further discipline does not give greater 

 loudness or wider range : on the contrary, increased vocal ex- 

 ercise, causing a waste in excess of repair, is often followed 

 by decrease of power. In the perceptions we see 



similar limits. The culture which exalts the susceptibility of 

 the ear to the intervals and harmonies of notes, will not 

 turn a bad ear into a good one. Life-long effort fails to 

 make this artist a correct draftsman, or that a fine colourist : 

 each does better than he did at first, but each falls short of 

 the power attained by some other artists. Nor is 



this truth less clearly illustrated among the more complex 

 mental p'owers. . Each man has a mathematical faculty, a 

 poetical faculty, or an oratorical faculty, which special educa- 

 tion improves to a certain extent. But unless he is unusually 

 endowed in one of these directions, no amount of education 

 will make him a first-rate mathematician, a first-rate poet, or 

 a first-rate orator. Thus the general fact appears to 



be, that while in each individual, certain changes in the 

 proportions of parts, may be caused by variations of function, 

 the congenital structure of each individual puts a limit to 

 the modifiability of every part. Nor is this true of 



individuals only : it holds, in a sense, of species. Leaving 

 open the question whether, in indefinite time, indefinite modi- 

 fication may not be produced ; experience proves that within 

 assigned times, the changes wrought in races of organisms 

 by changes of conditions fall within narrow limits. We see, 

 for instance, that though by discipline, aided by selective 

 breeding, one variety of horse has had its locomotive power 

 increased considerably beyond the locomotive powers of other 

 varieties ; yet that further increase takes place, if at all, at an 

 inappreciable rate. The different kinds of dogs, too, in 

 which different forms and capacities have been established, 

 do not show aptitudes for diverging in the same directions at 



