F. G. GUSTAFSON 19 



tured solution, was rinsed in distilled water^ to free it from any ad- 

 hering nutrient solution, before putting it in the apparatus. The 

 proper amount of material was then wound around the glass tube 

 dipping into the solution in the respiration tube and secured in this 

 position by tying it with a thread. This exposed the surface of the 

 fungus to the liquid and also kept it from moving about and insured 

 the smallest amount of mechanical injury. When the apparatus was 

 in motion the air bubbles passing through the solution containing the 

 organism carried the CO2 given off by the fungus into the indicator 

 tube, where the change in color was noted. 



In all experiments pH 7.75 was the starting point and pH 7.42 the 

 end-point. This gave the same range for every reading and a uniform 

 change of 0.33 pH. The time required to produce this change under 

 normal conditions varied from 2j to 3| minutes, depending upon the 

 amount and condition of the material. 



A number of preliminary experiments were performed without 

 giving the fungus any nutrient while they lasted. When no nutrient 

 was present the rate of respiration gradually fell below normal. For 

 this reason it was thought best to add enough food to keep the control 

 up to normal, so that any deviation from normal would be due to the 

 action of the salt under investigation. 



In starting an experiment the rate of respiration was first obtained 

 in a 0.1 per cent solution of dextrose in distilled water. Unless the 

 rate remained practically constant for at least 20 minutes in this so- 

 lution, the material was rejected. The rate obtained in the dextrose 

 solution is called the normal rate of respiration and in all calculations 

 is taken as 100 per cent. 



Several concentrations of dextrose were tried, but as all seemed to 

 give the same results 0.1 per cent was chosen, as low viscosity is ad- 

 vantageous in the prevention of foaming. When the reagent used 

 in the experiment was introduced the concentration of dextrose was 

 thereby diluted one-half, so that during the experiment with the re- 

 agent it was only 0.05 per cent. In the numerous controls which were 

 made the same thing was done, but no effect on the respiration was 



^ All water used in these experiments was distilled from a hard glass flask, and 

 canie in contact with hard glass only throughout the experiment. 



