On the Mechanical Conception of Nature. 653 



something independent of, and in some way added 

 to, the animal body, and not a mere expression 

 for the fluctuations in the type of the organism. 

 If, however, we conceive variability in this latter, 

 the true scientific sense, it is in no way " quanti- 

 tatively unlimited," nor are its limits even de- 

 termined by external influences, but essentially by 

 internal influences, i. e. by the underlying physical 

 nature of the organism. Darwin has indeed 

 already shown this in a most beautiful manner in 

 his investigations upon the correlations of organs 

 and systems of organs of the body. To make 

 use of a metaphor, the forces acting within the 

 body are in equilibrium ; if one organ becomes 

 changed this causes a disturbance in the forces, 

 and the equilibrium must be restored by changes 

 in other parts, and these again entail other modi- 

 fications, and so forth. Herein lies the reason 

 why the primary change cannot exceed a certain 

 amount if the restoration of the equilibrium is not 

 to be quite impossible. This is but a metaphor, 

 and I do not wish to assert that we are at present 

 in a position to formulate and demonstrate mathe- 

 matically for any particular case, how much an 

 organ can become changed in any one species 

 before an interruption of the internal harmony of 

 the body takes place. But such impossibility of 

 demonstration does not appear to me to furnish a 

 sufficient reason for regarding variability as the 

 expression of a directive power as an " innate 



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