115 



edge. The medium must be kept in a dark place because the color is re- 

 stored by the action of daylight. 



(e) Endo's Medium (Robinson and Rettger's Modification). 



Water 1,000 c. c. 



Agar (powdered) 25 grams 



Peptone (American brand) 10 grams 



Meat extract (Liebig's) 5 grams 



Sodium carbonate (10% sol.) 10 c. c. 



Lactose, c. p 10 grams 



Fuchsin (sat, alcoh. sol.) 5 c. c. 



Anhydrous sodium bisulphite (10% sol.) 10 c. c. 



Dissolve the agar, meat extract, and peptone. Make neutral to litmus 

 paper, steam in the autoclave at 12 to 15 pounds extra pressure for 35 to 

 40 minutes, filter through absorbent cotton and cheesecloth, add the sodium 

 carbonate solution, and heat for about 10 minutes in a boiling water bath. 

 Introduce the lactose and the fuchsin into the hot liquid. The medium 

 will now be brilliant red. Finally add the bisulphite solution. The hot 

 medium is light red in color, is filled into large test-tubes, 20 cubic cen- 

 timeters in each tube, and sterilized for five to seven minutes at 10 pounds 

 extra pressure. When the medium has cooled completely it should be 

 of a light pink or flesh color in the tubes, but transparent and practically 

 colorless in the large Petri dishes. The tubed agar may be kept for sev- 

 eral weeks in the refrigerator. 



(f) A Simplified Endo's Medium (Levine) The medium is pre- 

 pared as follows: 



Distilled Water 100 c. c. 



Peptone (Difoo) 10 grams 



Dipotassium phosphate (K 2 HP0 4 ) 2 to 5 grams 



Agar 15 to 30 grams 



The ingredients are boiled until dissolved and any loss due to evapora- 

 tion is made up with distilled water. 



No adjustment of reaction is made and filtration is not necessary if 

 the medium is to be used for streak plate cultures. 



Measured quantities are placed in flasks or bottles and sterilized for 

 15 minutes at 15 pounds. 



For use, the agar prepared as above is melted and the following ma- 

 terials added to each 100 c. c. of medium. 



20 percent lactose solution 1 gram or 5.0 c. c. 



10 percent (saturated) alcoholic solution of basic fuchsin 0.5 c. c. 



Freshly prepared 10 percent sodium sulphite solution 2.5 c. c. 



Plates are poured, allowed to harden in the incubator, and inoculated 

 in the ordinary way. 



(g) Fuchsin (Endo) Agar (Savage's Modification). 1. Peptone, 

 10 grams; Liebig's extract of beef, 10 grams; sodium chlorid, 5 grams, are 

 boiled up in an enamelled dish with 1 liter of distilled water. The mix- 

 ture is then poured into a flask, 30 grams of powdered agar added, and 

 the whole heated in the autoclave at 115 C. for one hour. The flask is 



