H. Maxavell-Lefroy 117 



fumes in the ground floor were then so strong that it was impossible to 

 stay and I had difficulty in getting out. So the house remained shut 

 for a total period of sixty-nine hours when it was then opened up. 



The occupiers moved in a few days later and the lady of the house, 

 who had waged war on the mites for years, searched and found live ones 

 in the books and in one attic. A few days later they were found also on 

 the banisters and on the piano. Apparently this was all and three 

 months later the lady of the house wrote : " We shall not need any 

 further fumigation for the present : indeed I am hopeful we are practically 

 free of the mites. I have seen none on the furniture for some time 

 though I fully expected to in the last week's warm weather." Two 

 months later the house was reported clear entirely. 



It seems likely that had the fumigation been repeated fourteen days 

 later, even on a milder scale, every ultimate mite would then have been 

 destroyed. It must be remembered that not only is there the egg as a 

 resistant stage but also the curious hypopial stage, in which the mite 

 encases itself and passes into a resting stage. In either of these forms 

 fumigation would scarcely kill all in the most sheltered positions. The 

 experiment showed (as far as one alone can), that: 



1. Cyanide and bisulphide can be used together. 



2. The escaping vapours are not offensive to neighbouring houses. 



3. Clas escape from an ordinary house is slow. 



4. Bisulphide vapour escapes slowly from ordinary ventilated floors 

 (these not being closed). 



5. The cost of fumigation is not excessive. 



6. Neither gas damages the contents of a house. 



7. A single application at these strengths may be sufficient, by de- 

 stroying practically all the mites and making further increase impossible. 



From observation of the results it appeared as if the bisulphide was 

 not very effective even at this strength : one larder was treated very 

 heavily with bisulphide as it contained food that might absorb the 

 hydrocyanic acid : yet here mites were found. 



The second case may be more shortly told. It was a two story 

 house of 18,000 cubic feet capacity, heavily infested with book-lice 

 {Psocidae), which were of the usual wingless type found in houses. The 

 infestation had lasted from April to August and was proving detrimental 

 to the health of the lady of the house. From an examination made 

 under the floor, it appeared as if the two foot space below the floor was 

 not well ventilated, was damp, the beams covered with fungus and the 

 whole formed the main breeding-place of the Psocids, which came up 



