PREVENTIVE MEASURES 185 



Formalin 



Ten years or more ago, when formaldehyd gas was 

 found to be a good germicide, experiments were made 

 with it against different insects without success; but 

 the evaporation of formalin has continued to be of use 

 in sick rooms. Quite by accident it was discovered by 

 different people, apparently in different parts of the 

 world, that a formalin solution is a good mixture with 

 which to poison flies in the house. So far as we know, 

 the first person in this country to ascertain this was 

 Mr. C. H. Popenoe, who at that time was at the Kan- 

 sas Agricultural College. In the summer of 1903, dur- 

 ing the prevalence of an unusual number of house flies, 

 while mixing a solution of formaldehyd for the pres- 

 ervation of insects (four per cent, formaldehyd, or di- 

 lution to ten per cent, commercial), a quantity of the 

 mixture was left in a mixing dish on the table. Sev- 

 eral flies were noticed to alight and drink of the mix- 

 ture, quickly succumbing to its influence. A quantity 

 was therefore placed on a deep plate and set upon the 

 table. This remained on the table all the afternoon, 

 and in the evening was surrounded by many dead flies. 

 The room was practically cleared of the pests. The 

 dish of formaldehyd was used many times during that 

 summer and in subsequent years with excellent effect 

 as a fly poison. The flies seemed not to object to the 

 presence of the formalin, drinking the water with avid- 

 ity and dying close to the plate or saucer, where they 

 were readily swept up. 



