ANTAGONISM 



135 



three may be made and called solution 1 (different mix- 

 tures may be called solution 2, etc. ) . To solution 1 various 

 amounts of D may be added and the results plotted as 

 shown in Fig. 55, in which the additive effect is expressed 

 by the dotted line and the growth in the mixtures by the 

 unbroken line. Antagonism at any point may be easily 

 expressed. For example, the antagonism at the point 



is (MO-MN)-^MN. 



By the method of mixing unequally toxic, pure solu- 



Sol. I 100 



25 



% 



D 



75 



100% 



FIG. 55. Method of expressing antagonism in mixtures containing more than three com- 

 ponents: three of the components (A, B and C) are combined into solution I and varioue 

 amounts of the fourth component (D) are added; the ordinates represent growth; the abscis- 

 sae represent the composition of the mixtures; thus at the point M the mixture contains 62.5 

 o.o. of solution 1 to each 37.5 c.c. of solution Z); the antagonism at M is ON -r MN. 



tions or by the method of keeping the concentration of one 

 salt constant while varying that of the others, the dotted 

 line would become a curved one. 



If we mix such solutions as NaCl 0.12 M and CaCl 2 

 0.164 M the antagonism curve resembles the one in Fig. 49. 

 If, however, we reduce the concentration by one-half 

 there will be less toxicity and in consequence the antag- 

 onism will appear less pronounced. In order to illus- 

 trate this, curves have been prepared which are diagram- 

 matic composites of the curves obtained by the use 

 of several pairs of salts ; these composite curves are shown 



