THE CULTIVATION OF BACTERIA. 79 



practicable, be protected from sudden draughts of cold air and 

 should be kept in a room having as equable a temperature as 

 possible. In large laboratories it is often found convenient to 

 use the whole of a small room as an incubator, heating it by a 

 gas stove, to which a gas regulator may be applied. 



Culture-tubes which are being kept in the incubator are 

 likely to become dry if their stay is prolonged. In such cases 

 they should be covered with rubber caps, tin-foil, seahng-wax, 

 paraffin, or some other device to prevent evaporation. If 

 rubber caps are used, they should be left in i-iooo bichloride 

 of mercury solution for an hour, and the cotton plugs should 

 be singed in the flame, before putting them on. (Fig. 21.) 

 The writer prefers rubber stoppers, which may be boiled and 

 stored in bichloride of mercury solution. Cut the cotton plug 

 even with the edge of the tube, singe it in the flame, push it 

 into the tube about i cm. and insert the rubber stopper. 

 CFig. 20.) 



Cultivation of Anaerobic Bacteria. 



The cultivation of anaerobic bacteria is done best in a medium 

 containing i to 2 per cent, of dextrose. The tube should con- 

 tain a large quantity of the culture-medium. Just before using, 

 the medium should be boiled for a few minutes. Inoculate the 

 tube after cooling, but while the medium is fluid. Anaerobes 

 may be cultivated in the closed arm of the fermentation-tube 

 (see Fig. 46), but the opening between the two arms of the tube 

 must be small. 



Buchner's Method for the Cultivation of Anaerobes: Into a 

 bottle or tube which can be tightly stoppered, pour 10 c.c. 

 of a 6 per cent, solution of sodium or potassium hydroxide, 

 for each 100 c.c. of air contained in the jar. Add one gram of 

 pyrogaUic acid for each 10 c.c. of solution. The culture- 

 tube is placed inside of the larger bottle or tube, supported 



