i9o8] POND—SOLUTION TENSION AND TOXICITY 249 



but reference to the tables shows that such a concentration of barium 

 is entirely without inhibitory effect upon the concentration of the 

 enzyme tried. So by calculation it is seen that mj 20^0 of potassium 

 is equicationic with copper w/2048, but reference to the table shows 

 that potassium of such concentration is not toxic. In order to leave 

 no doubt that cation concentration is not a determining factor in 

 toxicity to the extent that equicationic solutions are equitoxic, the 

 following tests were made. 



According to calculation, the following solutions arc equicationic : 

 copper and lead m/2048, potassium m 1 20^0, barium m/ig']i. 

 Instead of making the exact concentrations for barium and potassium, 

 it was assumed that if w/1024 and w/2048 do not inhibit, intermediate 

 concentrations would not. Examination of the results shows that 

 there is no basis for regarding equicationic solutions as even probably 

 cquitoxic. Neither of the concentrations of barium tried nor of potas- 

 sium are inhibiting, while both of copper and one of lead are. By 

 calculation it is easy to see that there is no fixed relation apparent 

 between equitoxicity and equicationic concentration. The exceptions 

 may be multiplied. Thus in the butyrate tests in my other paper, 

 copper w/512 and lead m/512 are equicationic, equidissociated, and 

 equitoxic. On the other hand, barium w/8 and copper w/512 are 

 equitoxic, but the relative number of cations per unit volume of those 

 elements in those concentrations is 38 to i . That is, in unit volume of 

 barium w/8 there are 38 cations as compared with i cation in unit 

 volume of copper w/512. The test shown in Table XXI with ethyl 

 acetate shows that equicationic solutions may totally inhibit or may 

 not inhibit at all according to the salts compared. 



According to the calculation from the conductivity tables, the fol- 

 lowing nitrates have a cation concentration of ?w/8o. 7: barium w/64, 

 copper w/70, lead ;;z/64, and potassium w/76. Reference to the 

 above test shows that all of those concentrations are included within 

 the limits of the test, and yet copper and lead totally inhibit, while 

 barium and potassium do not inhibit at all. 



DISCUSSION 



The attempt to correlate physiological action with certain physical 

 or chemical properties either of the ions or of the atoms has thus far 



