1901] MICROSCOPICAL JOURNAL. 269 
The conditions necessary to obtain this direct contact, 
however, can not always be obtained in actual practice. 
Rooms are frequently not tight enough to obtain the con-- 
centration of the gas required. The mosquitoes can not 
be held in direct contact with the gas, for their sense of 
self-preservation helps them to escape. The period of 
irritation, lasting several minutes even in the bell jar, 
‘enables the insects to hide in available places, such as 
the folds of garments, hangings, or fabrics, or in the 
cracks and crevices where the gas only reaches in a di- 
luted form. If the room is not thoroughly sealed, some 
of the mosquitoes will surely get away, for their instinct 
in finding tiny avenues of escape is remarkable. The es- 
cape of one infected mosquito might be the spark that 
- would rekindle an epidemic. 
In general, it may be stated that to succeed in killing 
mosquitoes in a closed space with formaldehyd gas, the 
following definite requirements are essential. A large 
volume of the gas must be liberated quickly, so that it 
may diffuse to all portions of the room in sufficient con- 
centration. The room must not have cracks and chinks 
where the insects will breathe the fresh air entering, es- 
pecially if these openings are to windward. The room 
must not have heavy drapery, clothing, bedding, or other 
fabrics, so disposed that the insects may hide in the folds, 
away from the full effects of the gas. 
In order to compare the merits of formaldehyd with 
sulphur dioxid gas in disinfection against mosquitoes, ex- 
periments were made by burning sulphur and with the 
liquid sulphur dioxid gas. 
The power of sulphur dioxid to destroy all forms of 
animal life is well known. On account of its destructive 
action upon fabrics and metals, this agent is of little 
practical use in the disinfection of dwelling houses, cab- 
_ins of ships, and similar places. This destructive action 
is due to the moisture which combines with the sulphur 
