32 



APPLIED BACTERIOLOGY 



The heat must be sufficient to keep the water in vigoroas 

 ebullition, so that the steam issues freely from the top. In 

 this way a uniform temperature of 100° C. is maintained in 

 the apparatus. The steriliser is fitted with a wire basket 

 or metal rack for the reception of test-tubes containing 

 nutrient media. 



This apparatus is employed for sterilising media and 

 apparatus which cannot be exposed to temperatures higher 



Fig. 3. — Steam Stekilisek. 



than that of boiling water (100° C). Glass and other 

 utensils may be steamed for from one to two hours ; but 

 some nutrient materials are unable to withstand the 

 temperature of 100° C. for any length of time. Thus 

 nutrient gelatine loses its power of solidifying on pro- 

 longed heating at the boiling temperature. Hence it is 

 advisable to expose media containing gelatine to a current 

 of steam for not more than fifteen minutes on three 

 successive days. The heating on the first day destroys all 



