3? 
are more resistant than the g'reat mass of them which are killed off 
by the 3 per cent solution, but these finally succumb to a 5 per cent 
solution. 
Table No. 28. — Ten per cent formalin {37.2 per cent aldehyde). 
Organism. 
Time of exposure to formalin. 
Control 
grew in — 
Minutes. 
Hours. 
10. 
20. 
30. 40. 
50. 
1. 
H- 
2. 
Vibrio cholera 
1 
24 hours. 
Do. 
Do. 
Do. 
Do. 
B. coli communis . 
B. diphtheriae 
- 
- 
- 
- 
- 
- 
- 
- 
B. mallei 
B. pvocyaneus 
B. dysenterise (Shiga) 
+' 
+ 
- 
- 
- 
- 
- 
- 
- 
Staphylococcus pyogenes albus 
Staphylococcus pyogenes aureus 
B. typhosus 
Only those organisms which resisted the 5 per cent solution for 
ten minutes were used. Of the nonspore-bearing organisms only 
B. dysenteride and Staphylococcus alhus survived an exposure of ten 
minutes to a 10 per cent solution of formalin. 
TIME OF MAXIMUM GERMICIDAL EFFECT. 
In order to study when the greatest germicidal action is exerted, 
pure cultures of the five most resistant organisms were exposed to a 2 
per cent and a 3 per cent solution of formalin. The dilutions were 
made just as in the preceding experiments, but instead of making 
plants in broth a loopful of the exposed culture was put into a full 
tube of melted agar, and then poured into a petri dish which, as soon 
as the agar had hardened, was placed in the incubator. 
The colonies were counted on the fourth da}L Plants were made at 
five-minute intervals, except in the case of B. pyocyaneus^ when 
exposed to 3 per cent formalin, and then plants were made at two- 
minute intervals. 
Table No. 29. — Two per cent formalin {37 per cent aldehyde, 1.8 acidity). 
Number of colonies grown at different intervals of exposure. 
Organism. 
At once. 
5 minutes. 
10 min- 
utes. 
15 min- 
utes. 
20 min- 
utes. 
30 
min- 
utes. 
40 
min- 
utes. 
50 
min- 
utes. 
60 
min- 
utes. 
B. dysenterise 
Innumerable . 
410 
22 
19 
5 
3 
1 
1 
1 
B, pyoevaneus. . .. 
do 
290 
1 
0 
0 
0 
R. t.vnhnsns 
do 
6,839 
Not count- 
213 
8 
1 
1 
0 
0 
0 
Staphylococcus 
genes albus. 
pyo- 
do 
7, 200 
4,800 
2,600 
800 
480 
63 
2 
able. 
Staphylococcus 
genes aureus. 
pyo- 
do 
1,080 
410 
94 
32 
9 
2 
0 
The above results show very plainly that in a 2 per cent solution the 
maximum effect is executed in the first five minutes, B. dysenteride 
and the cocci showing the greatest resistance. 
