ISOLATION OF ANAEROBES 453 



excellently on a given medium but its accompanying organisms 

 grow better than it does, try similar selective media of modified 

 reaction, or make use of exhaust media of the type recommended 

 by TuUoch. One may always grow the objectionable species or 

 several species in a medium till growth' ceases, filter the medium 

 and then grow the mixed culture in the filtrate. In case this fails 

 one may add a minute quantity of some solid protein for a starter. 

 Tulloch added a bit of rabbit kidney to an exhaust filtrate and 

 found it highly selective for B. tetani. Von Hibler grew mixtures 

 containing B. tetani on clotted rabbits' blood and stated it to be 

 selective for that organism. But his photographs of the organism 

 show his cultures to have been so badly contaminated that he 

 may have been mistaken. 



I have found a modification of a medium of Beijerinck's excel- 

 lent for the enrichment of soil anaerobes (sodium phosphate 0.05 

 per cent, ammonium sulphate 0.05 per cent, soluble starch 1 per 

 per cent, calcium carbonate 0.5 per cent). The anaerobic flora 

 obtained in such a medium after heating a soil emulsion is very 

 different from that obtained in meat or other media of complex 

 composition. By fishing large lenticular or modified lenticular 

 colonies from 2 per cent agar shakes of this medium which have 

 been incubated for four days, the large butyric acid bacteria of 

 the genus Clostridium may be isolated with comparative ease. 

 Winogradsky (1902) recommends the use of media free of fixed 

 nitrogen for the isolation of nitrogen fixing anaerobes ( Clostri- 

 dium Pastorianum) ; this medium is described by Fred (1916) 

 and Bredemann used it for the isolation of his Bacillus amijlo- 

 hacter which he considers to be the same organism as Winograd- 

 sky' s. Milk may also be used as an enrichment medium for many 

 organisms of this genus. 



Omeliansky (1904) describes the following method for enrich- 

 ing cellulose fermenters: Place in a long-necked flask any cel- 

 lulose substance, paper, cotton, flax; add chalk, and fill to the top 

 with water which contains 0.1 per cent ammonium phosphate, 0.1 

 per cent calcium phosphate, 0.05 per cent magnesium sulphate, 

 and a little sodium chloride. Inoculate with slime or horse ma- 

 nure, cover, and set in the dark. In other pubUcations (1895; 



