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, i. 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 Wiesuegg 

 (P. Lequeux), Paris. It is well made, very durable, quickly 

 sterilized, and easily operated if one can command an air-blast 



Fig. 40.* 



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. (or at the 



*FiG. 40. Simple method of obtaining small quantities of sterile fluids by means of the 

 Ohamiberland filter. The other end of the rubber tube is wared 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. 



