70 METHODS OF CULTIVATION OF BACTERIA 



to filter all the organisms from fluids in which they may have 

 been growing. This is done especially in obtaining the soluble 



toxic products of bac- 

 teria. The only filter 

 capable of keeping back 

 such minute bodies as 

 bacteria is that formed 

 from a tube of unglazed 

 porcelain as introduced 

 by Chainberland. The 

 efficiency of such a filter 

 depends on the fineness 

 of the grain of the clay 

 from which it is made ; 

 the finest is the Kitasato 

 filter and the Chamber- 

 land " B " pattern ; the 

 next finest is the Cham- 

 berland "F" pattern, 

 which is quite good 

 enough for ordinary 

 work. There are several 



filters, differing slightly 



FIG. 31. Geissler's vacuum pump arranged with 

 manometer for filtering cultures. (The tap 

 and pump are intentionally drawn to a larger . 

 scale than the manometer board to show 1 *" a11 P 01 



details.) the common principle. 



Sometimes the fluid is 



forced through the porcelain tube. In one form the filter 

 consists practically of an ordinary tap screwed into the top 

 of a porcelain tube. Through the latter the fluid is forced and 

 passes into a chamber formed by a 

 metal cylinder which surrounds the 

 porcelain tube. The fluid escapes 

 by an aperture at the bottom. Such 

 a filter is very suitable for domestic 

 use, or for use in surgical operating- 

 theatres. As considerable pressure 

 is necessary, it is evident it must be 

 put on a pipe leading directly from 

 the main. Sometimes, when fluids 

 to be filtered are very albuminous, FlG 32._Chamberland's candle 

 they are forced through a porcelain and flask arranged for filtration, 

 cylinder by compressed carbonic 



acid gas. For ordinary bacteriological work, filters of various 

 kinds are in the market (such as those of Klein and 



