THE BEGINNINGS OF LIFE. loi 



organism as a whole. The new sets of forces com- 

 pounded with all the antecedent sets of forces can but 

 inappreciably alter that moving equilibrium of functions 

 which all these antecedent sets of forces have estab- 

 lished. Though there may result a considerable 

 perturbation of certain functions — a considerable di- 

 vergence from their ordinary rhythms — yet the general 

 centre of equilibrium cannot be sensibly changed. On 

 the removal of the perturbing cause_, the previous 

 balance will be quickly restored, the effect of the 

 new forces being almost obliterated by the enormous 

 aggregate of forces which the previous balance ex- 

 presses 1.' Thus, variations which may be induced for 

 a time in higher organisms^ continually tend, when the 

 modifying influences have disappeared, to be dwarfed 

 and perhaps ultimately abolished, owing to the sum total 

 of internal forces acting in such a manner as gradually 

 to reproduce the former condition of equilibrium 2. 



But how different are the facts when we turn our 

 attention to lower organisms! Almost all naturalists 

 admit the greater amount and range of variability 

 amongst the lower forms of life, although we think 



* For a fuller explanation of the reasons why this should be than we 

 are able now to enter upon, we must refer the reader to Mr. Spencer's 

 ' Principles of Biology,' vol. i. pp. 192-198. 



^ It is this tendency which was formerly spoken of in medical works 

 as the vis medicatrix nattirce. Were it not for such a tendency, the success 

 ,of the physician in combating with internal diseases, or of the surgeon in 

 superintending wounds and injuries, would be much less manifest than 

 it IS at present. 



