84 METHODS OF CULTIVATION OF BACTERIA. 



bottom enables the filtrate to be removed without the 

 apparatus being unshipped. 



Before any one of the above apparatus is used, it ought 

 to be connected up as far as possible and sterilised in the 

 Koch's steriliser. The ends of any important unconnected 

 parts ought to have pieces of cotton-wool tied over them. 

 After use the bougie is to be sterilised in the autoclave, and 

 after being dried is to be passed carefully through a Bunsen 

 flame, to burn off all organic matter. If the latter is allowed 

 to accumulate the pores become filled up. 



The success of filtration must be tested by inoculating 

 tubes of media from the filtrate, and observing if growth 

 takes place, as there may be minute perforations in the 

 candles sufficiently large to allow bacteria to pass through. 

 Filtered fluids keep for a long time if the openings of the 

 glass vessels in which they are placed are kept thoroughly 

 closed, and if these vessels be kept in a cool place in the 

 dark. Sometimes the fluids may be evaporated to dryness 

 in vacua over sulphuric acid, and kept in an air-tight bottle 

 in a dry state. 



Instead of being filtered off, the bacteria may be killed 

 by various antiseptics, chiefly volatile oils, such as oil of 

 mustard (Roux). These oils are stated to have no injurious 

 effect on the chemical substances in the fluid, and they may 

 be subsequently removed by evaporation. It is not prac- 

 ticable to kill the bacteria by heat when their soluble pro- 

 ducts are to be studied, as many of the latter are destroyed 

 by a lower temperature than is required to kill the bacteria 

 themselves. 



The Observation of Bacterial Fermentations in Sugars. 

 The capacity of certain species of bacteria to originate 

 fermentations in sugars constitutes an important biological 

 factor. The end products of such fermentations may be 

 various. They differ according to the sugar employed and 

 according to the species under observation, and frequently 

 a species which will ferment one sugar has no effect on 

 another. The substances finally produced, speaking 

 roughly, may be alcohols, acids, or gaseous bodies (chiefly 



