ANTAGONISM 



125 



B 0.1 M the dilution of A from 0.1 M to 0.05 M is 

 exactly compensated by the introduction of molecules of 

 B. Or, to put it in another way, the toxic effect depends 

 on the number of molecules present (if both kinds of mole- 

 cules are equally toxic and 

 there is no antagonism) and 

 it makes no difference 

 whether the solutions are 

 pure or mixed. 



If the toxic effect depends 

 on ions, rather than on mole- 

 cules, then, since the number 

 of ions may be somewhat 

 increased by mixing solu- 

 tions, the toxicity may be 

 correspondingly increased; 

 but the amount of this 

 increase would ordinarily be 

 negligible. 



2. The toxicity is dimin- 

 ished, that is, the effect is 



We then get a 

 rising somewhere 

 the dotted line, such 

 the unbroken line LKM. 



3. The toxicity is 



We then get a c 

 which somewhere falls below 

 the dotted line, such as the line interrupted by cir- 

 cles LHM* 



The considerations here set forth apply in all cases 

 where two equally toxic solutions are mixed, whether their 



4 See page 177. 



111- 



FlG - 49. Curves showing the growth of 

 roots in mixtures of equally toxic solutions 

 of two salts A and B: the ordinatee represent 

 growth; the abscissae represent the composi- 

 tion of the mixtures, thus A 50, B 50 means 

 a mixture in which the dissolved molecules 

 are 50% .4 and 50% B: the horizontal dotted 

 ii ne (MM) represents the growth which 

 would occur if there were no antagonism 

 (additive effect); LKM is the antagonism 

 curve; LIIM, curve expressing increased 

 toxicity (opposite of antagonism); thequan- 

 titative expression of antagonism at the 



p int E is KJ^-JE. 



