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. 
