241 



BOTANICAL GAZETTE 



[APRIL 



In comparison with the preceding tables there are some points of 

 difference here. The reagent itself is acid and the unboiled prepara- 

 tions show a deposit of substance which tends to be zero in quantity 

 as the dilution of the reagent increases and the acidity consequently 

 decreases. The point of uninhibited activity Hes close to that of the 

 lowest concentration of the toxic solution having zero acidity. The 

 acidity of the control is greater than the sum of the reagent acidity and 

 the acidity of the enzyme solution. In this table (VIII) it will be 

 noted that the reagent acidity for w/32 cadmium is 0.30, while the 

 corresponding control figure is 0.90. A similar relation holds for 

 cobalt. The same relation was observed for these salts in the work 

 on ethyl butyrate. That cadmium and cobalt are more toxic than 

 sodium, potassium, Hthium, barium, strontium, and magnesium is 

 certain. Thus it appears that the first inhibitory effect in our series, 

 which seems more likely to be due to chemical action than to osmotic 

 surface tension or other physical influences, is associated with sub- 

 stances having a natural acidity. 



TABLE IX: Copper and zinc in contemporaneous test 



COPPER 



Water. 

 16384. 



8192. 



4096. 



2048. 



1024. 



Reagent 



0.00 

 0.05 

 o. 10 

 0.20 

 0.40 



Control 



Enzyme 



0.07 

 o. 10 

 0.13 

 o. 17 



0.23 



0.40 



o. 19 

 o. 19 

 o. 19 



O. 22 



o. 27 



0.40 



Increase 



0.12 

 0.09 

 0.06 

 0.05 

 0.04 

 0.00 



16384. 

 8192. 

 4096. 

 2048. 

 1024. 



Enzyme 0.05 per cent. Incubation 5 hours at 40 C. 



In this test copper and zinc are certainly equitoxic. Copper is 

 much more active in the precipitation of substance from the solution. 

 All the unboiled solutions with zinc were free from sediment after 

 incubation, showing that inhibition is not necessarily associated with 

 precipitation. In the copper solutions sediment was present in all 



