GENERAL BACTERIOLOGY 
107 
tone and 100 grams of best French sheet gelatin (“Gold 
Seal” brand). 
(b) Dissolve by heating, add water np to 1,000 c.c. 
(c) Cool to 60° C., add whites of two eggs, stir and 
heat for thirty minutes in Arnold’s sterilizer. 
(d) Add water up to 1,000 c.c. filter through cotton. 
Sterilize in autoclave for twenty minutes at 15 pounds 
pressure. 
(e) Do not slant this medium, as it is inoculated by 
• ‘ stabbing. ’ ’ 
9. Potato Media 
(a) Large potatoes are well washed and scrubbed with 
a nail brush. Peel and wash in running water. 
(b) Cylindrical pieces are removed with a large apple 
corer, and each cylinder is cut diagonally into two 
wedges. 
(c) Immerse the wedges overnight in 1 per cent solu¬ 
tion of sodium carbonate to correct the normal acidity. 
(d) Insert the wedges into test tubes (if desired they 
can be first soaked in 25 per cent glycerin—the glycerin 
potato medium). 
(e) Sterilize for thirty minutes in Arnold’s sterilizer 
on three successive days. 
10. Litmus Milk 
Litmus milk medium is used for determining the power 
of bacteria to curdle the milk and produce acid (as 
shown by fading of the blue color and the tube turning 
red). 
(a) Fresh milk is heated in a flask in Arnold’s steril¬ 
izer for fifteen minutes. 
(b) Put flask in ice box to allow the cream to separate. 
The cream is then syphoned off. 
