Sibyl T. Jewson and F. Tattersfield 239 



the cell are very slight. The toxicity of Pyridine does not arise out of its 

 modification of the ^H value of the medium but would seem in some 

 way to depend upon a special relationship of the cell to the Pyridine 

 molecule as a base. 



10. Practical Application of Method. 



The following method has been used in the treatment of mite infested 

 fungus cultures with Pyridine. A large bell-jar of about 20 litres capacity 

 is inverted and in the bottom is placed a flat dish containing about 20 c.c. 

 of commercial Pyridine and covered by a wire gauze. The infested cul- 

 tures, without removing the cotton- wool plugs, are placed in the bell-jar 

 for 16 hours (overnight) and the jar is closed with a glass plate which 

 should be luted down with clay or plasticine. Subcultures taken from 

 the tubes after the above treatment have proved free from the infesting 

 mites, except in one example described above, where some eggs appear 

 to have survived the above treatment, so that in the case of very bad 

 infestations or in very cold weather it may be advisable either to expose 

 the tubes for 48 hours or to give two exposures of 16 hours duration 

 separated by a period of fourteen to sixteen days. The latter method 

 allows any unkilled eggs to hatch, the very susceptible larvae being 

 rapidly poisoned by the second exposure to the vapour of Pyridine. 

 Owing to the rather disagreeable odour of Pyridine it is advisable to 

 carry out the treatment either in a good fume cupboard or outside the 

 laboratory. 



Strong Ammonia can be used for cleaning out laboratory apparatus. 

 Its toxic properties to mites are exceedingly great, but as it has a 

 sUght but definitely deleterious effect upon some fungi, it is advisable 

 to limit its use to apparatus when its vapour will not play for any pro- 

 longed period upon mycological cultures. 



Our best thanks are due to Mr H. M. Morris, M.Sc, for much valuable 

 advice and for identifying the species of mites, and to Mr E. M. Crowther, 

 M.Sc, for the determination of the ^H values of our media. 



11. Summary and Conclusions. 



1. Mites are a serious pest of fungus cultures. The species that most 

 frequently occur are Aleurobius farinae and Tyroglyjthus longior with an 

 occasional infestation with Glyciphagus cadaverum. 



2. They can be controlled by exposing the cultures to the vapour of 

 Pyridine, after which treatment the fungi can be subcultured safely. An 

 exact description of the application of the method is given on p. 239. 

 (Commercial Pyridine is as effective as the pure material.) 



