1. In the presence of 0.05 per cent dextrose the respiration of Aspergillus niger is increased by NaCl in concentrations of 0.25 to 0.5M, and by 0.5M CaCl2.
2. Stronger concentrations, as 2M NaCl and 1.25M CaCl2, decrease the respiration. The decrease in the higher concentrations is probably an osmotic effect of these salts.
3. A mixture of 19 cc. of NaCl and 1 cc. of CaCl2 (both 0.5M) showed antagonism, in that the respiration was normal, although each salt alone caused an increase.
4. Spores of Aspergillus niger did not germinate on 0.5M NaCl (plus 0.05 per cent dextrose) while they did on 0.5M CaCl2 (plus 0.05 per cent dextrose) and on various mixtures of the two. This shows that a substance may have different effects on respiration from those which it has upon growth.