Sibyl T. Jewson and F. Tattersfield 219 



tionated. The fraction distilling between 115° and 125° C. was again 

 treated with Permanganate and again fractionated. The fraction dis- 

 tilling between 114° and 117° C. was collected and tested quantitatively 

 for its toxicity to mites. The pure and commercial Pyridine were tested 

 for their toxic action to mites and their eggs. 



Two samples of cheese mites were obtained and identified as T. longior, 

 or a species very closely related to it. Both samples contained a large 

 number of eggs. Duplicate tubes of the mites were then treated in bell- 

 jars with {a) Pyridine (1 above), and (6) commercial Pyridine (3 above) 

 for a period of 16 hours, two controls being set aside over water for 

 purposes of comparison. At the end of this period they were examined 

 and in all the treated samples the mites showed no signs of Hfe. 



After a period of fourteen days all the samples were re-examined 

 with the result that whereas one of the controls showed many young 

 and lively mites and comparatively few unhatched eggs and the other 

 a few large live mites and a large number of unhatched eggs, the tubes 

 exposed to the vapoar of both samples of Pyridine contained no live 

 mites, either adults or newly hatched larvae. This and many subsequent 

 experiments amply proved that there is little or no difference in toxic 

 action between the costly pure Pyridine and the cheap commercial 

 article. 



6. Toxicity of Pyridine to the Eggs of Mites. ■ 



The critical point in the method is the toxicity of Pyridine to the 

 eggs of mites, for unless all are killed the infection is not eliminated. 

 This matter was therefore studied with considerable care, the actual 

 experiments being repeated several times to ehminate chance results due 

 to such factors as the Pyridine not penetrating a thick mass of mites or 

 to the sample undergoing desiccation during the aeration subsequent to 

 the experiment. 



The results in one case (Series I) do not agree with those obtained at 

 any other time, but they are set out in Table IVa wdth the purpose of 

 indicating that a sixteen-hour exposure which we have generally found 

 to be ample to kill all mites and eggs may fail in certain cases and as a 

 consequence we suggest that with very heavy infestations a second 

 exposure may be necessary after a period of fourteen days. 



Series I was exposed in duplicate for 16 hours to vapour of three 

 qualities of Pyridine. A little flour was placed in each tube to provide 

 a food supply for any larvae hatching out. After treatment both mites 

 and flour were transferred to fresh tubes and the excess of Pyridine 

 allowed to escape. The result was definitely negative and might be due 



