130 



■c Avc 0.500 a 



it, near x — U./D, z grows a, x grows ^^.0,-^; 



O.OoD 



■ç 1 or 0.500 a ^ 



ir, near x = I.zd, z grows a, x grows ^ ^^^o ^^c- 



That is; in order to find the growth of the varions 

 x's we hâve in our table to make the column z' which 

 gives the différences of the consécutive values of the z. 

 If then the growth of any of the z under the influence 

 of any one cause is a (the growth of ail the z being 

 equal), the growth of the x's will be 



0.500 a 



that is: the growth of any one x will be proportional to 



, 1 



the quantity -~ 



corresponding to that x. 



For Computing thèse reciprocals --r a table has been 



z 



given at the end of this paper (table 12). For reasons of 

 convenience and because a constant factor is absolutely 



immaterial, the table gives ' , instead of , . 



z z 



In table 2 the values of the x corresponding to thèse 



values of -*,- are those intermediate between the values 



z 



of the first column and it is for this reason that thèse 

 quantities (as also the z') hâve been printed between 

 the Unes. 



I will call reaction-curve the graphical représentation of 



the values of ', or V X const., because its ordinales 



r z 



represent the relative growth and fluctuations, in one 

 Word the relative amount of the déviations produced by 

 any one cause for the individuals of différent size x, that 



