44 BACTERIA IN RELATION TO PLANT DISEASES. 
of the cylindrical glass vessel. When sterilized and ready for use, select a piece 
of rubber cloth 10 or 15 cm. in diameter, cut a small slit in its center and draw 
it over the nipple of the bougie to protect the cotton from accidental wetting and 
the filtered fluid from consequent possible contamination. Now pour the fluid 
into the bougie (if one with a large neck has been selected this will not be difficult, 
especially if a small funnel is used and this is kept from close 
contact on one side by means of a small wire, sliver, or bit of 
paper), and connect the nipple with the outflow-tube of the 
compressed-air pipe by means of an extra-thick rubber tube, 
which should be securely wired at each end, and turn on the 
compressed air cautiously. Fluids which are not colloidal 
usually filter very readily with a pressure of 15 or 20 pounds 
per square inch. 
The filtering should always be done slowly with a mini- 
mum pressure in order to avoid the possibility of forcing small 
organisms through the walls of the filter. With heavy pressure 
this sometimes occurs when no cracks are detectable in the 
bougie. When the desired quantity of fluid has been filtered 
(fig. 40) cut off the air-blast, disconnect the tube, tilt the cylinder 
as much as possible, remove the bougie, and substitute the 
sterile cotton plug. The fluid should now be transferred 
immediately, in 5 or 10 cc. portions, to sterile cotton-plugged 
test-tubes by means of sterile pipettes. . The removal of the 
bougie and the transfer of the fluid should be done in clean 
still air, under a hood or in a special culture-room. ‘The tubes 
should not be used for several days, z. e., time should be given 
for contaminations to show themselves, but if proper care has 
been exercised there should be very few contaminations or 
none at all. A pressure much greater than 20 pounds per 
square inch may be obtained by means of steam-pumps or by 
use of cylinders of compressed air, oxygen, or carbon dioxide, 
and this is sometimes necessary for colloidal substances, but 
should be used cautiously. These cylinders may be had from 
the Eagle Oxygen Company, New York. One of the most 
convenient filters on the market is that shown in fig. 41. It 
was designed by Roux and is made by Maison Wiesnegg 
(P. Lequeux), Paris. It is well made, very durable, quickly 
sterilized, and easily operated if one can command an air-blast 
or other gas-pressure-of 2 or 3 atmospheres. 
Chamberland bougies ought not to be used continuously for more than three 
days. ‘They should then be removed and baked for two hours at 145° C. (orat the 
*Fic. 40—Simple method of obtaining small quantities of sterile fluids by means of the 
Chamberland filter. The other end of the rubber tube is wired securely to the outflow pipe of the 
compressed-air system and the fluid is forced from the inside of the filter out. This method was 
first described and figured by Dr. Theobald Smith. About one-fourth actual size, 
