Proposals on the Classification of Microor 'danisms 589 



name and it is impossible to determine tlie botanical or geo- 

 graphical source. One can only assume that in North America 

 the major source is an agar prepared from Gelidium cartUa^iineum 

 (16). In New Zealand, Davis agar, is prepared from Vlerodadia 

 capillaceae and F. lucida. Some agar in the U.S.S.R. is obtained 

 from Ahnfeldtia plicata. 



Many attempts have been made to define agar. The Society 

 for General Microbiology (13) re\'iewed the preparation and 

 properties of different agars and found that it was not possible 

 to lay down any standard specifications. The definition suggested 

 to the American Society for Microbiology in the Manual ol 

 Microbiological Methods (9) was that "Agar is any pliycocolloid 

 derived from the Rhodophyceae which gels at 33 to 39 C and 

 melts at 70 C." This definition will include preparations which 

 contain different polysaccharides. 



The agar from Gelidium amansii was shown to be a mixture 

 of a major component agarose and a minor component agaropec- 

 tin (2). Agarose consists of 1,3-linked /3-D-galactopyranose and 

 1,4-linked 3,6-anhydro-«-L-galactopyranose residues and is known 

 to occur in a number of different species of red algae ( 16 ) . 

 As a result of these studies it is now possible to suggest the follow- 

 ing definition. 



Agar is a mixture of polysaccharides which is deri\ed fronr 

 certain species of the Rhodophyceae and which contains the 

 polysaccharide agarose. The preparations which are supplied for 

 bacteriological purposes should meet the specifications suggested 

 by the committee on Bacteriological Technic of tlie American 

 Society for Microbiology. 



It is highly desirable that commercial preparations sliould 

 indicate the botanical and geographical source of the algae used 

 to prepare the agar. 



Species of the Rhodophyceae which contain agarose wxv 

 listed in Table 1. The concentration of agaropectin or other 

 polysaccharides in the extracts obtained from these algae is not 

 known. The species in which carrageenan is found are listed in 

 Table 2. This polysaccharide \ields a gel whicli may be used 

 under certain conditions as a substitute for agar. 



