272 THE AMERICAN MONTHLY [Oct 
Mosquitoes have a lively instinct in finding cracks or 
chinks where fresh air may be entering the room, or 
where the gas is so diluted that they escape destruction, 
They are able to escape through incredibly small open- 
ings. Some of the smaller varieties, such as the stegomyia 
fasciata can get through a wire screen having 12 meshes 
to the inch. Therefore, formaldehyd gas can not- be 
trusted to kill all the mosquitoes in a room which can not 
be tightly sealed. 
It is concluded, that to succeed in killing all the mos- 
quitoes in a closed space with formaldehyd gas, the fol- 
lowing definite requirements are essential: A very large 
volume of the gas must be liberated quickly, so that it 
may diffuse to all portions of the space in sufficient con- 
centration. The room must have all the cracks and chinks 
where the insects may breathe the fresh air carefully 
sealed by pasting strips of paper over them. The room 
must not contain heavy folds of drapery, clothing, bed- 
ding, or fabrics in heaps, or so disposed that the insects 
may hide away from the full effects of the gas. 
Sulphur dioxid is unexcelled as an insecticide. Very di- 
lute atmospheres of the gas will quickly kill mosquitoes. 
It is quite as efficacious for this purpose when dry as when 
moist, whereas the dry gas has practically no power 
against. bacteria. Contrary to formaldehyd it has sur- 
prising powers of penetrating through clothing and fa- 
brics, killing the mosquitoes, even when hidden under 4 
layers of toweling, in one hour’s time—and with very 
dilute proportions. | 
This substance, which has so long been disparaged asa 
disinfectant because it fails to kill spores, must now be 
considered as holding the first rank in disinfection 
against yellow fever, malaria, filariasis, and other insect- 
borne diseases. A pamphlet giving in detail all the ex- 
periments by which the above conclusions were reached 
can be had from the Marine Hospital Bureau. 
