84 BACTERIOLOGICAL METHODS 



loop is made as follows: Bend the end of a No. 27 platinum wire? 

 10 cm. long, around a piece of No. 10 wire. The free portion of 

 the straight platinum wire inoculating needle, shall be 10 cm. 

 long (No. 27 wire). The standard fermentation tube shall be 

 of the following proportions. The length of the closed end of the 

 fermentation tube (diameter about 1.5 cm.) shall be about 14 cm., 

 and the open end shall be of bulbous form (diameter of bulb about 

 3.8 cm.) large enough to hold all of the liquid in the closed end. 

 Larger and smaller fermentation tubes than the standard just 

 described may be used for special purposes. Standard and other 

 fermentation tubes may or may not be graduated as the special 

 purposes may require. 



2. Amounts of Media to be Tubed. The standard amount of 

 culture medium to be placed in each test-tube of standard size is 

 5 and 10 cc., the media to be introduced by means of a suitable 

 burette. Greater or lesser quantities may be used as occasion 

 may require. Tubes containing just 10 cc. of culture media are 

 required for the plating purposes. 5 cc. quantities (of gelatin, 

 agar and other solid media) are required for making slants. 



3. Amounts of Culture Media to be Plated. For the usual 

 quantitative determinations by the plating method, 10 cc. of the 

 culture medium shall be poured in each standard Petri dish. 



The required number of tubes each containing 10 cc. of agar or 

 gelatin culture medium are placed in the steam sterilizer until 

 the medium is entirely liquefied and then placed in a beaker or other 

 suitable container with lukewarm water, with thermometer. 

 Plate the gelatin medium when the thermometer registers be- 

 tween 25 and 30 C. The temperature of the medium must not 

 be more than 30 C. If the temperature is less than 25 C. the 

 gelatin will begin to coagulate and will not pour and spread 

 properly. Agar media must be plated at a higher temperature 

 than gelatin media, usually 40 to 42 C. The Petri dishes should 

 be warm when the media are poured, the temperature being ap- 

 proximately the same as that of the medium when it is poured. 



