STORING MEDIA 



159 



walls being filled with water at about 90 C. and 

 supporting the latter on a ring gas burner fixed to a 

 retort stand (Fig. 101). The gas is lighted and the 

 water jacket maintained at a high temperature until 

 filtration is completed. If the steam steriliser of the 

 laboratory is sufficiently large, it is sometimes more 

 convenient to place the flask and filtering funnel bodily 

 inside, close the steriliser and allow filtration to proceed 

 in an atmosphere of live steam, than to use the gas ring 

 and hot- water funnel. 



STORING MEDIA IN BULK. 



After filtration fill the medium into sterile litre flasks 

 with cotton-wool plugs and sterilise in the steamer for 

 twenty minutes on each of three 

 consecutive days. After the 

 third sterilisation, and when the 

 flasks and contents are cool, cut 

 off the top of the cotton-wool 

 plug square with the mouth of 

 the flask; push the plug a short 

 distance down into the neck of a b 



the flask and fill in with melted d( S^ stoT^le ."", bS 

 paraffin wax to the level of the fore > and b > after sterilizing. 

 mouth. When the wax has set the flasks are stored 

 in a cool dark cupboard for future use. 



This plan is not' absolutely satisfactory, although 

 very generally employed on occasion, and it is prefer- 

 able to fill the medium into long-necked flint glass 

 bottles (the quart size, holding nearly 1000 c.c., such as 

 those in which Pasteurised milk is retailed) and to 

 close the neck of the bottle by a special rubber cap. 1 

 This cap is made of soft rubber, the lower part, 

 dome-shaped with thin walls, being slipped over the 

 neck of the bottle (Fig. 102, a) . The upper part is solid, 



1 This rubber cap has been made for me by the Holborn Surgical Instnr 

 ment Co., Thavies Inn, London, W. C. 



