160 A MANUAL OF BACTERIOLOGY 



If neither electricity nor gas be available, an acetylene 

 bicycle lamp may be utilised. Failing all these, the 

 microscopist will have to fall back on a good paraffin 

 or other oil lamp, special forms of which are sup- 

 plied lor microscopical work but are not essential. 

 (Bunsens working with spirit are procurable, so that 

 the Barnard mantle lamp might be used in the absence 

 of gas.) 



A bull's-eye condenser on stand is a useful adjunct, 

 as by means of it the light from any source may be 

 collected and focussed on to the mirror. 



The light, from whatever source, may be modified in 

 various ways. A smoked or blue-tinted glass may be 

 interposed, and many condensers are fitted with a special 

 cell to hold a disc of the tinted glass. Monochromatic 

 light filters are supplied by the Kodak Co. A narrow 

 glass cell filled with a coloured solution may also be 

 employed. Such a cell may be constructed by placing 

 a piece of rubber tubing (|-| in. diameter) between two 

 pieces of clear sheet glass and clamping the two plates 

 together with a couple of strong spring paper clips. The 

 rubber tube is bent round so as to form the bottom and 

 edges of the cell. The whole is supported in a wooden 

 stand or with a wooden burette clamp. The best solutions 

 to employ in such a cell are (1) for blue light, ammoniacal 

 copper sulphate solution ; (2) for green light, a solution of 

 chromic acid and of nitrate of copper, mixed in suitable 

 proportions (the larger the proportion of the copper 

 salt the greener the tint) ; (3) for yellow light, either 

 chromate of potash or picric acid. 



The round glass flask filled with water tinged with 

 ammoniacal copper solution, already referred to, gives a 

 beautifully soft light. The mercury vapour lamp may 

 also be used in combination with the special screens 

 made by the Kodak Co. for use with this light, so that 



