420 BACTERIOLOGICAL ANALYSES 



bolted together by thumb screws through the over- 

 hanging flanges. When in use, place the bottles, rolled 

 in cotton-wool, in the central chamber, pack the space 

 between the walls with pounded ice, securely close the 

 metal box by screwing down the fly nuts, and place it 

 in a felt-lined wooden case. (It has been shown that 

 whilst bacteria will survive exposure to the temperature 

 of melting ice, practically none will multiply at this 

 temperature.) 



On reaching the laboratory, the method of examina- 

 tion consists in adding measured quantities of the 

 water sample to several tubes of nutrient media pre- 

 viously liquefied by heat, pouring plate cultivations 

 from each of these tubes, incubating at a suitable tem- 

 perature, and finally counting the colonies which make 

 their appearance on the plates. 



Apparatus Required: 



Plate-levelling stand. 



Case of sterile plates. 



Case of sterile pipettes, i c.c. (in tenths of a cubic centimetre). 



Case of sterile pipettes, 10 c.c. (in tenths of a cubic centimetre). 



Case of sterile capsules, 25 c.c. capacity. 



Tubes of nutrient gelatine. 



Tubes of nutrient agar. 



Tubes of wort gelatine. 



One 250 c.c. flask of sterile distilled water. 



Tall cylinder containing 2 per cent, lysol solution. 



Bunsen burner. 



Grease pencil. 



Water-bath regulated at 42 C. 



METHOD. 



1. Arrange the plate-levelling platform with its 

 water compartment filled with water, at 45 C. 



2. Number the agar tubes, consecutively, i to 6; 

 the gelatine tubes, consecutively, i to 6, and the wort 

 tubes, i, 2, and 3. Flame the plugs and see that they 

 are not adherent to the lips of the tubes. 



3. Place the agar tubes in boiling water until the 



