MEDIA 27 



After the medium is filtered and tubed we add i% of lactose and i% of a i-ioo 

 neutral red solution. Colon colonies have a distinct purplish red zone. Furthermore 

 the bile inhibits the growth of many organisms which give pink colonies on lactose 

 litmus agar. MacConkey's bile salt medium contains 1/2% of sodium taurocholate 

 and is colored with neutral red. 



THALMAN'S MEDIUM FOR THE GONOCOCCUS. 



Five hundred grams of lean, finely minced beef are placed in 1000 c.c. of distilled 

 water and allowed to stand over night in an ice box. It is then filtered and the fil- 

 trate made up to 1000 c.c. with distilled water. To 100 c.c. of the beef juice add 

 i 1/2 grams of agar, and boil for 15 minutes. Then add 2 grams of glucose, and bring 

 the reaction to plus 0.6 by addition of N/iNaOH. Tube, sterilize, slant, and in- 

 cubate over night. No peptone or salt is required. 



PLATING MEDIA FOR F^CES WORK. 



The media of Endo, Conradi-Drigalski and the lactose litmus agar medium are 

 probably the most satisfactory of the numerous ones that have been proposed for 

 plating out faeces. A convenient way of preparing any one or all of these, and which 

 apparently gives media equal to that prepared according to the original formulae, 

 is as follows: 



Liebig's extract, 5 grams. 



Salt, 5 grams. 



Pep ton, 10 grams. 



Agar, 30 grams. 



Water to make 1000 c.c. 



Prepare as for ordinary nutrient agar, with the difference that the reaction should 

 be brought down to o. Some prefer a reaction of +0.2. 



A stiff agar (3%) is employed to check the diffusion of acid beyond the colony. 



FOR ENDO'S MEDIUM. 



Keep this agar base in 100 c.c. quantities in Erlenmeyer flasks instead of test- 

 tubes. (If more convenient smaller quantities may be put in the flask.) When 

 needed for plating, melt a flask of this agar, and while liquid add to the 100 c.c. 

 six drops of a saturated alcoholic solution of basic fuchsin, and then about twenty 

 drops of a Treshly prepared 10% solution of sodium sulphite. The sulphite solution 

 decolorizes the intense red of the fuchsin to a light rose pink. This color fades to a 

 light flesh or pale salmon color when cold. Now add 5 c.c. of a freshly prepared 

 hot aqueous 20% solution of chemically pure lactose. If only occasionally using 

 such media, tube in 20 c.c. quantities and add one drop of the basic fuchsin and four 

 drops of the sodium sulphite solution and i c.c. of the hot freshly prepared lactose 

 solution to a tube of the melted agar base just before pouring the plate. This medium 

 contains i% of lactose. Kendall prepares an Endo medium which only contains 

 i 1/2% of agar and with a reaction just alkaline to litmus (about plus 1.2%). 



