290 DIFCO MANUAL 



SOLDIFYING AGENTS 



BAGTO-AGAR (B140) 



The introduction of agar-agar as a solidifying agent for culture media was an 

 important step in the advancement of the science of bacteriology. Credit for the 

 use of agar for this purpose is generally given to Fannie Hesse. ^-^ Agar media 

 have made possible many of the advances of bacteriology, for the use of these 

 solid media paved the way for our present day methods of pure culture isolation 

 and study. 



Bacto-Agar is a purified agar from which the extraneous matter, pigmented 

 portions, and salts are reduced to a minimum. Bacto-Agar is available in the form 

 of fine, light-colored granules, which are convenient for weighing and handling. 

 It is usually employed in solid culture media in concentrations of 1-2 per cent. 

 Recently the use of small quantities of agar (0.05-0.3 per cent) in media has 

 become quite general for the determination of motility and the growth of 

 anaerobes and micro-aerophiles. The addition of such amounts of agar to liquid 

 media, as discussed under Bacto-Brain Heart Infusion on page 77, permits all 

 degrees of oxygen tension to exist and thus aids in the development of many 

 fastidious aerobic and anaerobic organisms. 



The value of the use of small quantities of agar in media for sterility testing 

 was pointed out by Falk, Bucca and Simmons^ and has been incorporated in 

 the thioglycollate medium for sterility testing of biologies and antibiotics by 

 official procedures.*'^'®''^ 



^ Hueppe: Die Methoden der Bakterienfor- ^ Compilation of Regulations for Tests and 



schung, 1891. Methods of Assay and Certification of Anti- 



2 J. Bact., 37:485: 1939. biotic Drugs, Federal Security Agency, Food 



5 J. Bact., 37:121 :i939. and Drug Administration. 



•♦National Institute of Health Circular: Culture ^Pharmacopeia of the United States, XIV Re- 

 Media for the Sterility Test, and Revision, vision: 758: 1950. 

 Feb. 25, 1946. ' National Formulary, 9th Edition: 768: 1950. 



SPEGIAL AGAR (NOBLE) (B142) 



Special Agar (Noble) is a carefully washed agar, free from all impurities 

 which would interfere with its efficiency when employed in the preparation of 

 Noble's^ Cyanide Citrate Agar, for the direct plating and counting of the coli- 

 aerogenes group. It is prepared according to the procedure suggested by Noble 

 and each lot is tested for its usefulness in the preparation of his medium. Noble 

 and Tonney- specify the use of Special Agar (Noble) as an ingredient of their 

 Brilliant Green Lactose Bile Agar for the direct plate count of the coliform group 

 in water. The medium, Bacto-Brilliant Green Bile Agar, is discussed on page 52. 



^ J. Am. Water Works Assoc, 19:182:1928. ^ j_ Am. Water Works Assoc, 27:108:1935. 



B AGTO-GELATIN ( B 1 43 ) 



Gelatin was first employed as a solidifying agent for bacteriological culture 

 media by Koch in 1881. This innovation paved the way for the future of the 

 science although gelatin media were soon replaced by others containing agar as 

 the solidifying material. 



