222 Infestation of Fungus Cultures by Mites 



In Series III the lethal chambers were conical flasks of about 1200 c.c. 

 capacity. Small samples containing many eggs and a few mites (100 to 

 28) were placed in small tubes, the mouths of which were covered with fine 

 silk gauze, and suspended in the vapour in the flask at a temperature of 

 18°-19° C. for varying lengths of time. The flasks were hermetically 

 sealed by lead-lined rubber stoppers. After exposure the samples were 

 poured out into small flat dishes and exposed to the atmosphere for 

 15 to 30 minutes until the odour of Pyridine had almost disappeared. 

 They were then placed in a large bell- jar containing a basin of water 

 and left overnight, after which they were transferred to tubes with the 

 addition of a little flour and kept at 18°-19° C. in a moist atmosphere. 



Two samples of Pyridine, one practicall}^ chemically pure, the other 

 labelled commercial, were tested in this way for times ranging from three 

 hours, which is just long enough to eUminate the mites, to 72 hours. It 

 is of interest to note that in every case except the controls, the samples 

 became covered with a mat of fungus mycelium, indicating that httle 

 danger to fungus growth is to be feared from exposures up to 72 hours. 

 Examination was carried out from time to time up to 28 days. Three 

 hours' exposure was quite ineffective against the eggs, practically all 

 hatching out in 16 days; 8 hours was partially successful as many eggs 

 did not hatch in 20 days, while 16 hours and upwards completely pre- 

 vented hatching out. No difference whatever could be detected in the 

 lethal properties of the two samples of Pyridine. It is considered that 

 if the treatment be carried out at an equable temperature of about 

 18°-20° C, 16-24 hours' exposure should be sufficient to ehminate both 

 mites and eggs. It is recognised, however, that there may be cases of 

 heavy infestation when the vapour of Pyridine may not be able to per- 

 meate completely and where a second exposure after fourteen days 

 might be advisable before subculturing. 



7. Action op Pyridine on Mites (Quantitative). 



An attempt was made to put the results on a quantitative basis. 

 This was deemed advisable because of the rather surprisingly high 

 toxicity of Pyridine in air saturated with its vapour and because materials 

 like Aniline and Dimethylanihne which, from the work of Tattersfield 

 and Roberts (3), were expected by us to have a higher toxic value in the 

 vapour phase than Pyridine had proved of doubtful value. Pyridine, 

 Ammonia and Aniline were therefore compared. For this purpose flasks 

 of about 1100 c.c. capacity were fitted with lead-lined rubber stoppers, 

 through which passed a glass rod turned to a hook at the lower end, to 



