Sibyl T. Jewson and F. Tattersfield 223 



which could be attached a short test tube by means of wire. The first 

 series of experiments was carried out in air saturated with the appro- 

 priate vapour. In the case of Pyridine and Anihne a few drops in excess 

 of what was required to saturate the atmosphere were pipetted into the 

 flasks. After a time sufficiently prolonged to allow of the air being 

 saturated, the tubes containing the mites and closed at the top by a 

 little silk fabric of very fine mesh, drawn tight and fastened firmly to 

 prevent the mites from escaping, were inserted by attaching to the hooks 

 and pushing the cork home. With Ammonia 5-10 c.c. of -880 material 

 was poured in; in this case the toxic action is so rapid as to render the 

 silk fabric unnecessary. Two controls were used for each set of experi- 

 ments. After varying lengths of time, in the case of Ammonia reckoned 

 in seconds, the tubes were taken out and either examined immediately 

 or after a time. 



The method of examination and the time that should elapse before 

 it is carried out were matters of considerable difficulty and need some 

 consideration. It is necessary to count at least a hundred mites to obtain 

 reliable results. Preliminary experiments showed olive oil to be the best 

 medium in which to count the mites under the microscope as they remain 

 alive in it for one to two hours and its clearing action is marked. Those 

 mites which on careful examination showed no sign of movement were 

 regarded as dead. If inspection be carried out immediately after expo- 

 sure there is a possibility of mistaking temporary anaesthesia or stupe- 

 faction for death. Experience showed, however, that this difficulty was 

 not very serious, for the poisons tested appear to act on the motor nerves 

 and a mite once thoroughly incapacitated in this way seems rarely to 

 recover. As a matter of fact, immediate examination gives an under- 

 estimation of the toxic action — but this can hardly be avoided. The 

 dangers of allowing the material to stand overnight appear more serious 

 as even when aerated in open dishes it loses such toxic materials as 

 Pyridine and Aniline only after a little time and at different rates owing 

 to differences in their respective vapour pressures, during which time 

 the poison continues to act. Moreover, in this treatment there is a 

 danger of desiccation, and of some non-poisoned eggs hatching out. 



The effect of Pyridine was tested in two ways. The examination in 

 one case was carried out immediately. In the other the treated mites 

 were aerated in the open till the characteristic odour had disappeared; 

 they were then kept for a further sixteen hours in a moist atmosphere, 

 after which they were examined. In the case of Ammonia examination 

 was carried out immediately and after the lapse of an hour or two during 



