F. G. GUSTAFSON 



189 



concentrations, such as Haas'^ reports using, had no effect whatsoever. 

 The lowest concentration that showed any effect was 0.5 per cent 

 (Fig. 5, Curve A). This gave a decrease in respiration from the 

 beginning. In the first two periods there was a decrease of nearly 

 20 per cent below normal; then followed several periods with hardly 

 any decrease at all. Several experiments with a saturated solution 



RATE 



\S0% 



Fig. 4. Curve B shows the respiration of Aspergillus niger, first for 20 minutes 

 in tap water (horizontal unbroken line), then for 9.5 minutes in 7.3 per cent ether, 

 then for 130 minutes (interval shortened in figure to save space and denoted by- 

 dotted lines) in nutrient solution, and finally for 36 minutes in tap water (un- 

 broken line). Curve A shows the respiration of a control placed in tap water for 

 30 minutes, then for 130 minutes in nutrient solution (dotted line), then for 34 

 minutes in tap water (unbroken line). The normal rate (which is taken as 100 

 per cent) corresponds to a change from pH 7.60 to pH 7.25 in 3 minutes. Aver- 

 age of three experiments. Probable error less than 2.4 per cent of the mean. 



of caffeine were also performed. An initial increase amounting to 

 about 15 per cent above normal was noticed (Fig. 5, Curve C). This 

 was followed by a gradual decrease till a rate of 60 per cent of the 

 normal was reached, when the rate of respiration became stationary 

 and remained so till the end of the experiment (over half an hour). 



^Haas, Science, 1917. xlvi, 462. 



