54 A MANUAL OF BACTERIOLOGY 



steam in the steam steriliser or the autoclave, the heating 

 and cooling being conducted slowly. 



Culture Media 



The ordinary methods of preparing culture media are 

 here given, but " Standard " media, having definite 

 reactions, are now largely employed (for the method of 

 standardisation, see p. 64). Certain special media will be 

 described as required. In all cases the media are filled 

 into the cleansed and sterilised vessels, test-tubes, flasks, 

 etc. (p. 53). For ordinary laboratory cultures test-tubes 

 are generally used. Media which are solid at ordinary 

 temperatures, e.g. agar, gelatin, and serum, are prepared 

 either as deep, upright tubes (Fig. 8, A), for which 8-15 c.c. 

 of the medium are required for a tube, or as sloping tubes 

 (Fig. 8, c), for which 4-5 c.c. are required for a tube. Of 

 fluid media 7-15 c.c. are used for a tube. The prepared 

 media having been introduced into the test-tubes, etc., 

 sterilisation is effected in the steam steriliser (p. 46) by 

 steaming for twenty to thirty minutes on two or three 

 successive days, or in the autoclave (p. 47) by heating to 

 115-120 C. for half an hour on one occasion. Culture 

 media may also be kept in bulk in flasks ; these need 

 somewhat longer sterilisation than tubes. Tubes of some 

 of the culture media can also be purchased ready for use. 

 Certain media can be obtained in powder form (Chopping's) 

 from Messrs. Baird and Tatlock, and in tabloid form 

 (Thompson's) from Messrs. Burroughs and Wellcome. These 

 are convenient when small quantities are required for 

 occasional use. 



Acid beef-broth. The basis of the most important 

 culture media, viz. peptone beef-broth, gelatin, and agar- 

 agar, is an infusion of meat prepared usually from beef. 

 In order to prepare this infusion, which may be termed 



