128 LABORATORY GUIDE IN BACTERIOLOGY 



solution to nutrient agar containing i per cent, glucose to 

 produce a clear red color without adjusting reaction. 



Litmus-broth. — Add litmus-solution to ordinary broth in 

 the proportion of lo per cent. 



Glycerin-agar. — Add 6 per cent, pure glycerin to nutrient 

 agar. 



Beerwort- gelatin — Autoclav beerwort at 120° for 5 min- 

 utes to precipitate proteids. After cooling, filter, dissolve 10 

 per cent, gelatin, and clarify with white of egg. 



Beerwort-agar. — Prepared like beerwort-gelatin, substi- 

 tuting ij per cent, agar in the place of gelatin. 



Blood-agar. — A drop of blood, obtained with aseptic 

 precautions, is smeared on the surface of slant-agar. 



Litmus-whey (Petruschky, modified by Durham). — 

 Casein is precipitated from milk with rennet-extract; the 

 whey is neutralized with 4 per cent, citric-acid solution and 

 heated on the water-bath for half an hour. It is then filtered, 

 and litmus-solution is added until a decided blue color is 

 obtained. 



Whey-gelatin. — Add 10 per cent, gelatin to clarified whey. 



Alkaline blood-serum (Lorrain Smith). — Add 1-1.5 per 

 cent, of a 10 per cent, solution of sodium hydrate to blood- 

 serum, tube, and sterilize in Arnold or in Koch's serum 

 inspissator. 



Bread-paste medium. — Bread is cut into slices, dried in 

 the oven, and pulverized; it is then distributed in 100 c.c. 

 flasks until the layer on the bottom is half an inch thick. 

 Water is gradually run in to cover the surface of the bread 

 Sterilize in Arnold. 



Mac Conkey's bile-salt-agar. — 



Nutrient agar 100 c.c. 



Sodium taurocholate 0.$% 



Peptone 2.0^ 



This is boiled, clarified, and filtered, and then 2 per cent, 

 lactose is added, tubed, and sterilized in the medium. 



