50 
this was especially so with the spores of B. subtilis exposed by the 
Wilson method. The reason for this is not apparent, since the tem- 
perature and humidity were practically the same in the different 
experiments. , 
In the following experiment (No. 26) the germicidal power of the 
formaldehyde was much diminished as a result of the low humidity— 
46 per cent — before starting the experiment. 
EXPERIMENT NO. 26. 
Autoclave. 
Formalin, 600 c. c.; glycerin, 60 c. c.; calcium chloride, 120 grams; water sufficient to make 1,000 
c. c. 
Capacity of room, 2,000 cubic feet. 
Quantity of formaldehyde used per cubic foot, 0.107 gram. ' 
Time required to exhaust material in autoclave, 22 minutes. 
Yield of formaluehyde, undetermined. 
Weather: Rather strong westerly wind. 
Tempera- 
ture. 
Relative 
humidity. 
Absolute 
humidity 
(grams per 
cubic foot) . 
• 
Before beginning to introduce the gas 
° F. 
68 
Per cent. 
46 
3.45 
After 30 minutes 
69 
67 
5.17 
After 2 hours 
69 
60 
4. 63 
See Note, experiment No. 23. 
[4- means growth; — no growth.] 
Organism. 
How exposed. 
B. pyocyaneus 
Glass 
B typhosus 
do 
B. staph, py. aureus 
do 
B. coli communis 
do 
B. pyocyaneus 
Filter paper 
B . coli communis 
Wilson method 
Time of exposure in min- 
utes, and results. 
5 
15 
30 
45 
60 
120 
180 
+ 
+ 
+ 
+ 


+ 
+ 
+ 
- 
— 
- 
+ 
+ 
+ 
+ 
- 
- 
+ 
+ 
+ 
+ 
— 
— 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
When working at reduced temperatures the same decrease in per- 
centage yield of formaldehyde and the same deficiency in germicidal 
action are observed in this method as in the formalin-permanganate 
and the retort methods. This is shown in the following two experi- 
ments, in which the spores of B. subtilis were not usually killed within 
3 hours, although the nonspore-bearing organisms exposed directly 
on slips of filter paper were killed in a fairly short time. 
Comparing the results of these two experiments with experiment 
No. 26, it will be seen that a reduction in humidity diminishes the 
killing power of formaldehyde more than does a similar reduction in 
temperature. 
