ENDO'S MEDIUM 33 



Subject these slants to temperature of 75C. on the second and third days for one 

 hour. 



PLATING MEDIA FOR FAECES 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. 



Pepton 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. 

 6 drops of a saturated alcoholic solution of basic fuchsin, and then about 20 drops 

 of a freshly prepared 10% solution of sodium sulphite. The sulphite solution de- 

 colorizes 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 i drop of the basic fuchsin and 4 

 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 me- 

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

 tains iH% of agar and with a reaction just alkaline to litmus (about plus 1.2%). 



Colon bacilli show on this medium as vermilion colonies, which in about forty- 

 eight hours have a metallic scum on them. Typhoid and dysentery colonies are 

 grayish. Streptococci a deep red. 



FOR LACTOSE LITMUS AGAR 



Color the 100 c.c. of agar base with litmus solution to a lilac color. Then add 

 5 c.c. of the hot freshly prepared 20% lactose solution in distilled water. This 

 may be tubed, putting 10 c.c. in each test-tube, or put in quantities of 50 or 

 100 c.c. in small Erlenmeyer flasks. It is then sterilized in the autoclave (10 

 pounds for fifteen minutes) or in the Arnold. 

 3 



