CULTURAL WORK OX THE FUNGUS. 



27 



Experiment No. 21. 



1,300 c. c. formalin per 1,000 cubic feet of air space. 

 Temperature before mixing reagents. 76° F. 



Thielaviopsis cultures in petri dishes. 



Initial Vigorous 



growth growth 



of fun, -us. of fungus. 



Checks; fungus not exposed to formaldehyde gas 



Fungus exposed IS minutes 



Fungus exposed 30 minutes 



Fungus exposed 60 minutes 



Hours. Hours. 



>\> 



40 



























Table I. — Results of experiments icitJt petri-dish cultures of Thielaviopsis. 



No. of experiment. 



Formalin 



per i .000 



cubic 



Temper- 

 ature be- 

 fore mix- 



feet. 



ing 

 reagents. 



c. c. 



°F. 



800 



72 



850 



72 



900 



72 



950 



72 



9.50 



78 



1,000 



74 



1,000 



78 



1.050 



65 



1,0.50 



75 



1,100 



66 



1.100 



75 



1.100 



78 



1.1.50 



75 



1,150 



66 



1,150 



76 



1.200 



70 



1.200 



78 



1.200 



78 



1 . 250 



76 



1.250 



80 



1.300 



76 



Retardation * of initial growth 

 of the fungus exposed to for- 

 maldehyde gas for 15. 30. and 

 00 minutes, respectively. 



Hours. 

 23 



Hours. 

 63 



40 



67 



72 



100 



94 







45 



118 



123 



123 







143 



97 















198 















74 



139 



196 



220 



43 



211 











































3 











v> 



Hours. 

 91 



119 



144 

 

 



212 

 

 



167 

 

 

 

 

 

 

 

 

 

 

 

 



* As previously stated, the retardation periods arc reckoned from the first indication of 

 growth in any single culture of any set of checks. 



The results of the experiments with petri-dish cultures of Thie- 

 laviopsis show that formaldehyde gas is effective in retarding the 

 growth of the fungus. The irregularities in the results obtained from 

 fifteen-minute exposures suggest that exposures of less than thirty 

 minutes are useless. There was no experimental evidence to show 

 the effect of variation in temperature and humidity on the fungicidal 

 property of the gas. but it is believed a that a high temperature and 

 humidity increase its efficiency. Although the amount of moisture 

 in the air of the room before starting any experiment was nearly 

 uniform, the temperature was varied as shown in the tabulations, 

 thus insuring comparable conditions with those encountered in actual 

 practice, where temperature will necessarily be a variable factor. 



McClintic. Op. cit., p. 71. 



171 



