402 TRUE AND Gries: HEAvy METALS 
retardation of the growth-rate without bringing it to a standstill. 
Of the compounds present, therefore, the calcium salt only entered 
in a concentration representing the stimulus phase. The marked 
effect following the entrance of the calcium and the potassium 
may, in part, be due in these experiments to the cumulative in- 
crease of concentration of the solution, with the corresponding 
decrease in the rate of ionization and the diminished number of 
active ions. The fact that the potassium salt, although added in 
a concentration hindering growth when taken singly, increased 
the growth-rate when added to the mixture as its last member, 
seems to strengthen this supposition. Of course, changes of this 
nature represent changes in the solution itself and lie outside of 
the cell, and should not be confused with the mutually antagonis- 
tic intracellular action of ions in the case of very dilute solutions. 
