STANDARD MEDIA 8 1 



settle. Add 10 grams of peptone and 5 grams of Liebig's meat 

 extract. Heat in rice cooker until the ingredients are entirely 

 dissolved. Neutralize with sodium carbonate, using litmus as 

 an indicator, and then add 10 cc. of a 10 per cent, solution of 

 sodium carbonate. 



Store the medium in lots of 100 cc. using flasks large enough 

 to permit the addition of the other ingredients. Sterilize for 2 

 hr. in streaming steam. 



To use the Endo medium proceed as follows: Make a 10 

 per cent, aqueous solution of sodium sulphite and add 2 cc. of 

 fuchsin solution (10 per cent, of basic fuchsin in 96 per cent, 

 alcohol) to 10 cc. of the sulphite solution and steam this mixture 

 for a few minutes in the steam sterilizer. Add i gram of chemically 

 pure sterilized lactose to each 100 cc. of the Endo medium after 

 the medium has been liquefied and while the temperature is not 

 above 60 C. While the medium is still liquid, add 0.5 cc. of 

 the fuchsin-sulphite solution and then pour into the Petri plates 

 and allow to harden in the incubator. The sulphite solution 

 must be prepared fresh as needed. 



10. Milk. The milk to be used for cultural purposes must be 

 pure and recently drawn. In all cases the milk of the grade or 

 quality known as "certified milk" is to be preferred. The 

 recently drawn milk is to be placed in the refrigerator for 12 

 hr., so as to permit the cream to rise to the top and any sus- 

 pended matter to sink to the bottom. Skim the milk and siphon 

 off all but the bottom sedimentary portion. Adjust to -f-i.o per 

 cent. Tube and sterilize. 



Litmus milk is made by adding i per cent, of sterilized azo- 

 litmin to the above. In using litmus milk always set aside a 

 control tube with the inoculated tubes for purposes of color 

 comparison. 



Because of the difficulty of always getting a uniformly high 

 quality of cow's milk, it has been suggested that an artificial 

 substitute be employed. Hill and his pupils recommend a 



