52 A MANUAL OF BACTERIOLOGY 



up to where it was heated before, and draw out again 

 and seal off two or three inches from the bulb. In this 

 way a capillary tube with a bulb at its middle is formed 

 (Fig. 7). " Vaccine tubes," pipettes made of glass tubing 

 drawn out at one end, and Wright's capsules (see Fig. 35, 

 a and d, p. 215) are also useful. 



India-rubber caps. A few indiarubber caps for capping 

 test-tube or flask cultures are required. They retard 



FIG. 7. Glass pipette. 



evaporation and the desiccation lof the medium, and 

 prevent the entrance of moulds. For use they should be 

 soaked in 1-500 corrosive sublimate solution; they 

 should not be kept pn the solution, as vulcanised rubber 

 absorbs mercuric chloride (Glenny and Walpole). Tinfoil, 

 gutta-percha tissue (sealed down by warming), paraffin 

 wax, sealing wax, or plasticine may also be used to cover 

 the tops of tubes and flasks. 



Preparation of Sterile Test-tubes, Flasks, etc., 

 for the Reception or Manipulation of Cul- 

 ture Media 



To sterilise cotton-wool. Non-absorbent cotton-wool, 

 best or No. 2 quality, is used for plugging purposes. The 

 wool should be pulled apart so as to assist the penetration 

 of heat ; in the compressed condition the interior is 

 difficult to sterilise The separated wool is placed in the 

 hot-air steriliser and the temperature is slowly raised to 

 145 C. and maintained at this for at least an hour. Above 

 150 C. cotton-wool becomes brown and brittle. It is a 

 common practice now to use various coloured wools for 

 the different culture media, especially the carbohydrate 



