F. G. GUSTAFSON 



185 



were made with this concentration. Their average happens to cor- 

 respond almost exactly with one experiment, and this experiment 



30MIN. 



Fig. 1. Curve showing the effect of 0.4 per cent formaldehyde on the respira- 

 tion of Aspergillus niger. The shaded portions represent the periods during 

 which respiration was measured. The unshaded portions represent the interven- 

 ing time during which no measurement was made (e.g., time spent in changing 

 the material from one solution to another) . The horizontal part of the curve shows 

 the normal respiration; the remainder the respiration in 0.4 per cent formalde- 

 hyde. The dotted line represents the respiration of a control in tap water. Time 

 is reckoned from the beginning of the exposure to formaldehyde. The normal 

 rate (which is taken as 100 per cent) corresponds to a change from pH 7.60 to 

 pH 7.25 in 2.75 minutes. 



was used instead of the average in drawing the curve, as will be seen 

 in Fig. 1. The periods during which the measurements were made 

 are indicated by shading. The rate which is obtained for each period 



