18 
! 
The mosquitoes and the cultures were exposed in the pill boxes with 
gauze lids, under similar conditions, as follows : 
Mosquitoes. 
Bacteria. 
Dead. 
Alive. 
Subtilis 
spores. 
Pyocya- 
neus. 
In pill boxes : 
On floor, under carpet 
7 
0 
T 
In canvas mail sack, folded 
5 
0 
— 
In pocket duck coat, hung up 
5 
0 
_i_ 
— 
In pocket cloth trousers, hung up 
5 
0 
-f 
— 
Under 2 lavers drv toweling 
9 
0 
Lost. 
— 
Under 2 lavers damp toweling 
0 
— 
— 
Wrapped tight! v in drv towel, 7 lavers 
6 
0 
— 
— 
Wrapped tightlv in moist towel, 7 layers 
4 
0 
— 
In coat pocket, hung up, flap closed 
6 
0 
— 
In bottom of 12-inch beaker covered with 2 lavers of towel.. 
4 
0 
— 
— 
In corner of folded newspaper, under 7 lavers .. 
8 
0 
The results were the same as No. 14, viz, death of all mosquitoes, 
even when well protected by dry or moist fabrics ; the death of fresh 
moist cultures of pyocyaneus, and the failure to affect subtilis spores 
similarly protected. 
No. 16. 
A series of experiments was made to determine whether chemically 
dry sulphur dioxid has insecticidal properties. It is well known that 
the anhydrous gas has practically no effect upon bacteria. As the dry 
gas is not destructive to fabrics and metals, it is of considerable prac- 
tical importance to know whether it will kill mosquitoes. 
To this end the liquid sulphur dioxid was liberated in a bell jar, but 
first passed through 2 drying columns containing pumice stone satu- 
rated with sulphuric acid. The moisture contained in the air of the 
bell jar was eliminated in 2 ways, (1) by drawing air through the 
drying columns into the bell jar, or (2) by introducing calcium chlo- 
rid into the bell jar. 
It was found, in all these tests, that the mosquitoes were killed, prac- 
tically, instantly by the dry gas. 
Contrary to formaldehyd, which requires an exposure and strength 
of gas sufficient to destroy spores in order to entirely rid a room of 
mosquitoes, sulphur dioxid will kill these insects even when the quan- 
tity of the disinfectant and the time of exposure are reduced so that 
non-spore-bearing bacteria are unharmed. 
Sulphur dioxid was for a long time used as a disinfecting agent 
against yellow fever, and experience found it to be trustworthy. But 
later it was^disparaged because laboratory tests showed that it lacked 
the power of killing spores and has little penetrating power through 
fabrics. But now that we know it is the mosquito which carries the 
infection, the usefulness of this agent is revived. 
