102 
PRINCIPLES OF BACTERIOLOGY 
special bacterial filters (Berkefeld’s or Chamberland’s) 
which are made of unglazed porcelain or earthenware. 
Slanting of Media. —The solid culture media, after 
Fig. 19.—Tubing the media. 
they have been sterilized, usually are slanted, that is, the 
tubes are laid down on a desk or table so that the upper 
end of the test tube rests on a ledge or glass tubing, in 
