164 BIOLOGY AND TECHNIQUE 



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

 in isolating them from other sources. Jackon and Melia 36 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 frac- 

 tional method. 



MacConkey's Bile-Salt Agar: 



Sodium glyeocholate 0.5 per cent. 



Pepton 2.0 " " 



Lactose 1.0 ' ' " 



Agar '. ... 1.5 " " 



Tap water q.8. 



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

 glyeocholate 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 

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



Bariekow's Medium* 1 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 NaCI, 10 grams of lactose, and sufficient aqueous litmus 

 solution to give a pale blue color. 38 



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. 

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

 reaction 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. 



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



87 BarsieTcow, Wien. klin. Bund., xliv, 1901. 



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



* g Kussell, Jour. Med. Kesearch, xxv, 1911, 217. 



