Sibyl T. Jewson and F. Tattersfield 



217 



Table II. 



Action of the Vapour of Certain Organic Chemical Compounds 

 on Mites (Aleurobius farinae). 



Chemical 

 Pyridine (1) Pure 

 „ (2) 



(3) Commer'l. 



Action after 3-4 hours 



After 4 hours all mites ap- 

 peared dead. Some of larger 

 ones recovered a day later 

 and some eggs hatched out. 



Aniline 



Monomethylaniline 



Dimethylaniline 



Naphthalene 

 p-Dichlorbenzene .. 



Carbon bisulphide 



No apparent effect. 

 All anaesthetised. 



Action after 16 hours 

 All appeared dead. 



All appeared dead. 



Many appeared dead but most 

 of the large and some small 

 ones moved sluggishly. 



A few of both large and small 

 ones alive but sluggish. 



Large mites alive but sluggish. 



No apparent effect. 



All apparently anaesthetised 

 but some recovered on ex- 

 posure to air. 



All apparently dead. 



All apparently dead. 



An inspection of Tables I and II clearly indicates that for practical 

 purposes Pyridine is much the most hopeful compound. Carbon bisul- 

 phide, although apparently rapid in its action, is too toxic to fungi to 

 be useful, while Paradichlorbenzene, which, from its slight poisonous 

 action on fungi and from the almost complete absence of disagreeable 

 properties, would have been an ideal substance to apply, seems to have 

 only a pronounced but temporary anaesthetic effect. 



In view of these results it was decided to make a more complete 

 study of the toxic action of Pyridine and to ascertain, if possible in a 

 quantitative way, its reaction with both mites and some common fungus. 



5. The Quality of the Pyridine used in the Experiment. 



Four samples of Pyridine were tested for their effect upon mites and 

 fungi. 



1. A sample labelled pure Pyridine. 



2. A sample obtained by a rough fractionation of commercial 

 Pyridine. 



3. Commercial Pyridine. 



4. A sample carefully purified in the Laboratory. 



No. 2 sample was intermediate in quality between samples 1 and 3. 



The testing of these grades was regarded as necessary owing to the 

 wide discrepancy in price between pure and commercial Pyridine. It 

 was also essential to ascertain whether through the presence of any 



