MOIST HEAT 



33 



5. Destroy these new vegetative forms by a similar 

 exposure to 56 C. on the second day, whilst others, 

 of slower germination, may be caught on the third day, 

 and so on. 



6. In order to ensure thorough sterilisation, repeat 

 the process on each of six successive days. 



This method of exposing liquids to a temperature 

 of 56 C. in a water-bath for half an hour on each of 

 six successive days is termed fractional sterilisation. 



Water at 100 C. destroys the vegetative forms of 

 bacteria almost instantaneously, and spores in from 



FIG. 27 . Water sterilizer. 



five to fifteen minutes. This method of sterilisation 

 is applicable to the metal instruments, such as knives, 

 forceps, etc., used in animal experiments; syringes, 

 rubber corks, rubber and glass tubing, and other small 

 apparatus, and is effected in what is usually spoken of 

 as the "water steriliser" (Fig 27). 



This is a rectangular copper box, 26 cm. long, 18 cm. 

 wide, and 12 cm. deep, mounted on legs, heated from 

 below by a Bunsen or radial gas burner, and containing 

 a movable copper wire tray, 2 cm. smaller in every 



