CULTURAL WORK OX THE FUNGUS. 21 



development of the fungus, therefore the critical and final work was 

 concerned with quantities varying from 750 to 1.300 c. c. per 1.000 

 cubic feet of air space. 



CULTURAL WORK ON THE FUNGUS. 



For the cultural phase of the work the method was to isolate the 

 fungus and grow pure cultures which were subjected to the direct 

 action of the formaldehyde gas. Corn-meal agar proved a very 

 satisfactory medium and was used throughout the experiments, during 

 which over 1.500 cultures were made. Those intended for fumiga- 

 tion were smear cultures made in petri dishes. These dishes were 

 well adapted to the purpose, as their shape permitted an equal dis- 

 tribution of the gas over their surface. Checks were made from 

 the cultures immediately before they were subjected to the treat- 

 ment, and transfers directly after. 



Some authorities have contended that a dormant period precedes 

 the germination of the maerospores, but in the present investigations 

 no such condition was observed. Immediate germination was proved 

 by transferring a definite number of maerospores from vigorously 

 growing cultures to petri dishes containing 8 to 10 c. c. of media or 

 by making drop cultures and noting the germination of the indi- 

 vidual >pores. Whether this is a cultural peculiarity due to favorable 

 media or some other congenial condition can not be stated, as there 

 was no opportunity for field observations on the behavior of the 

 fungus or character of the infections under natural conditions. 



EXPERIMENTS WITH PETRI-DISH CULTURES. 



In each of the experiments in petri dishes many cultures were 

 submitted to the action of the formaldehyde gas for different lengths 

 of time, and a corresponding number of transfers were made after 

 fumigation. In giving a record of the results of the effect of the 

 gas, the initial or macroscopically visible and vigorous growths noted 

 were in each case those of the first transfer showing any indication 

 of growth. The data presented in the following tables show the 

 minimum fungicidal effect of the gas. not the average period of 

 retardation or the average number of cultures which grew. The 

 period of retardation was estimated as the difference betAveen the 

 time of the initial growths of the checks and the fumigated material. 

 The time of exposure is taken from the time the reaction commenced. 



171 



