18 
In this manner plants into tubes of nutrient bouillon were made 
at different intervals when so desired. The tubes were placed in 
the incubating room at a temperature of 37° C. and the results 
recorded after ten days’ incubation. 
Other methods of exposing organisms, such as placing slips of 
contaminated filter paper in envelopes and in small paper boxes in 
which numerous holes had been punched, were tried for the purpose 
of testing the penetrating power of formaldehyde, but the results 
were so unsatisfactory that the methods were abandoned. 
The Wilson method affords a very simple and convenient way of 
exposing organisms to the action of a gaseous disinfectant, and in 
case it is impracticable to make the plants immediately after making 
the exposures they can be taken to the laboratory and planted 
without much risk of outside contamination. 
DISINFECTANTS AUTHORIZED BY U. S. QUARANTINE REGULATIONS AND THE PROPER 
METHODS OF GENERATING AND USING SAME. 
FORMALDEHYDE GAS. 
163. Formaldehyde gas is effective if applied by one of the methods 
given below. Formaldehyde gas has the advantage as a disinfectant 
that it does not injure fabrics or most colors. It is not poisonous to 
the higher forms of animal life. It fails to kill vermin such as rats, 
mice, roaches, bedbugs, etc. The method is not applicable to the 
holds of large vessels. Formaldehyde is applicable to the disinfection 
of rooms, clothing, and fabrics, but should not be depended upon for 
bedding, upholstered furniture, and the like, when deep penetration is 
required.® 
164. Many formaldehyde solutions do not contain 40 per cent of 
formaldehyde, and all are apt to deteriorate with time. It is therefore 
necessary to use a quantity in excess of the amount prescribed in these 
regulations, unless the solution has been recently ‘analyzed. 
165. The following methods of evolving the gas may be used: 
(a) Autoclave under pressure, 3 to 12 hours’ exposure. 
( b ) Lamp or generator, 6 to 18 hours’ exposure. 
(c) Spraying, 12 to 24 hours’ exposure. 
0 d ) Formaldehyde and dry heat in partial vacuum, 1 hour’s expo- 
sure. 
166. The minimum number of hours’ exposure as given above ap- 
plies to empty rooms of tight construction containing smooth, hard 
surfaces; the maximum number of hours’ exposure applying in all cases 
to textiles and other articles of a similar kind requiring more or less 
penetration. 
1 67. Autoclave under pressure. This method has considerable pene- 
trating power when applied as detailed below. Rooms or apartments 
a It should be noted that formaldehyde disinfection is more efficient in warm, moist, or 
still weather than in cold, dry, or windy weather. 
