138 BIOLOGY AND TECHNIQUE 



Melia l found that in this medium B. typhosus and B. coli outgrow all 

 other microorganisms and eventually B. typhosus will even outgrow B. coli. 

 It consists of sterilized undiluted ox-bile (or a ten per cent solution of dry, 

 fresh ox-bile) to which is added one per cent pepton and one per cent lactose. 

 It is filled into fermentation tubes and sterilized by the fractional method. 



MacConkey's Bile-Salt Agar. 



Sodium glycocholate 0.5 per cent. 



Pepton 2.0 " " 



Lactose .' 1 .0 " " 



Agar ,. 1.5 " " 



Tap water V(^V~- Q- s - 



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

 sodium glycocholate added before tubing. The B. typhosus produces no 

 change; B. coli, producing acid, 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 color- 

 less by reduction of the neutral-red and produce gas. 



Barsiekow's Medium. 2 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. 3 



Russell's Double Sugar Agar.* Russell has devised a simple medium for 

 quick identification of typhoid bacilli. 



A 2% or 3% extract agar is used, about 0.8% acid to phenolphthalein 0.8%. 

 Enough litmus solution is added to give it the ordinary deep blue. The re- 

 action is then adjusted with sodium hydrate until neutral to litmus. Finally 

 1% lactose and 0.1% glucose (dissolved in a small amount of hot water) are 

 added, the medium is carefully sterilized in the Arnold sterilizer and slanted. 

 Inoculations are made by surface streak and stab. The typhoid bacillus grows 

 colorless on the surface, but under the imperfect anaerobic conditions at the 

 bottom of the stab, a bright red. color is developed by acid formation. 



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

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



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



2 Barsiekow, Wien. klin. Rund., xliv, 1901. 



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



4 Russell, Jour. Med. Research, xxv, 1911, 217. 



