CHAPTER IV. 

 ANTAGONISM. 



When one toxic substance acts as an antidote to 

 another, we speak of this as antagonism. If the antagon- 

 istic substances are mixed in such proportions that tox- 

 icity disappears we have a physiologically balanced 

 solution as defined by Loeb.^ 



In seeking an accurate measure of antagonism the 

 writer made experiments on growth. It was found t^^ 

 both NaCl and CaClg are toxic to plants, as shown by um 

 fact that in solutions of these substances there is less\ 

 growth than in distilled water .^ In a series of expei^j 

 ments on wheat, it was found that the growth of.rooti-^ 

 in NaCl 0.12 M was practically the same as in CaCl, 0.164 

 M. These solutions were therefore regarded as 

 equally toxic. 



On mixing equally toxic salt solutions, we may 

 encounter one of the following conditions :^ 



1. The toxicity is unaltered, that is, the toxic action 

 of the two salts is additive. Each salt produces its own 

 toxic effect precisely as though the other were not present. 

 This is expressed by the horizontal dotted line LJM in 

 Fig. 49. 



It is evident that we cannot get increased growth by 

 mixing two such solutions unless the salts have an antag- 

 onistic action. If we mix equal volumes of A 0.1 M and 



^ Cf. Loeb, J. (1906, B). For the literature of antagonism see Loeb 

 (1909), Robertson (l9lO), H6ber (1914). 



' This statement does not apply to very dilute solutions. 

 'Cf. Oaterhout (1914, B, C; 1915, F). 



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