138 BIOLOGY AND TECHNIQUE 



Jackson's Lactose-Bile Medium.^ — Jackson has devised a medium 

 now in general use by water-analysts, which is of great use in isolating 

 B. typhosus and B. coU from water, and serves as a valuable enriching 

 medium in isolating these organisms from other sources, such as feces. 

 Jackson and Melia ^ have found that in this medimn B. typhosus and B. 

 coli outgrow all other microorganisms and that eventually B. typhosus 

 will even outgrow B. coli. 



It consists of sterilized undiluted ox-bile (or an eleven per cent 

 solution of dry, fresh ox-bile) to which have been added one per cent 

 pepton and one per cent lactose. It is filled into fermentation tubes 

 holding 40 c.c, and steriUzed by the fractional method. 



MacConkey's Bile-Salt Agar. — 



Sodium glycocholate 5 per cent. 



Pepton 1.5 " " 



Lactose 3.5 " " 



Agar 1.5 " " 



Tap water q.s. 



The agar and pepton are dissolved and cleared and the lactose and 

 sodium glycocholate added before tubing. In this medium the B. 

 typhosus produces no change; B. coH, by producing acid from the 

 lactose, causes precipitation of the bile salts. 



Neutral-Red Medium. — To 100 c.c. of a one or two per cent glucose 

 agar add 1 c.c. of a saturated aqueous solution of a neutral-red. 



The medium is used in tubes, stab or shake cultures. The typhoid 

 bacillus produces no change, while members of the colon group render 

 the medium colorless by reduction of the neutral-red and produce gas 

 by fermentation of the sugar. 



Barsiekow's Medium.^ — To 200 c.c. of cold water, add 10 grams of 

 nutrose and allow to soak for one-half to one hour. Pour this into 800 

 c.c. of boiling water, and heat for twenty minutes in an Arnold sterilizer 

 at 100° C. Filter through cotton and to the opalescent solution of 

 nutrose add 5 grams of NaCl, 10 grams of lactose, and sufficient aqueous 

 litmus solution to give a pale blue color .^ 



Dieudonne's Selective Medium for cholera spirillum. See page 584. 



Enriching Substances Used in Media. — For the cultivation of micro- 



^ Jackson, "Biol. Studies of Pupils of W. T. Sedgwick," 1906, Univ. Chicago 

 Press. 



' Jackson and Melia, Jour. Inf. Dis., vi, 1909. 



' Barsiekow, Wien. kUn. Rund., xliv, 1901. 



^ Filtration may be done through paper, but takes a long time. 



