232 MICROSCOPIC AND CULTURAL STUDY OF BACTERIA 
50° C. for one-half hour to destroy enzymes. Two parts of hydrocele 
or ascitic fluid to S or 10 parts of plain nutrient agar previously melted 
and cooled to 45° C. make a medium especially adapted to the growth 
of many of the more fastidious pathogenic bacteria.^ 
Ascitic broth is prepared by adding 20 to 50 per cent by volume 
of sterile ascitic fluid to plain nutrient broth. Incubate to prove 
sterility. 
Egg Media. — Eggs are a very good substitute for blood serum in 
Loffler's medium. Eggs are carefully broken into a clean beaker, 
stirred gently with a rod (avoiding the formation of air bubbles) 
until homogeneous and mixed with glucose broth in the proportion 
of 1 part by volume of broth to 3 volumes of egg. The medium is 
coagulated in a slanted position and sterilized precisely as Loffler's 
blood serum is coagulated and sterilized. 
Egg Medium.— yio. 1. Mix 4 to 6 volumes of thoroughly homo- 
genized eggs with 1 volume of nutrient broth, and add sufficient 
glycerin to make the concentration of the latter 3 per cent by weight. 
Coagulate and sterilize in the slanted position precisely as Loffler's 
blood serum is coagulated and sterilized. This medium is excellent 
for the cultivation of tubercle bacilli. 
No. 2. Add 1 volume of physiological salt solution to 2 volumes of 
egg which have been lightly stirred with a rod until the yolks and 
whites are intimately incorporated. Coagulate and sterilize in a 
slanted position in test-tubes. 
Milk and Litmus Milk. — One liter of fresh milk is thoroughly mixed 
and tubed in the ordinary manner. Litmus milk is prepared by 
adding sufficient litmus solution to impart a clear blue color. It is 
tubed, using 10 cc. to each tube, and sterilized in the autoclave. 
For some purposes it is desirable to remove the cream before tubing, 
but for cultural work the color of the cream ring in litmus milk is of 
some diagnostic importance. Thus, members of the paratyphoid 
group of bacilli almost invariably show a blue-green cream ring; the 
colon bacillus colors the cream ring red-brown. It should be remem- 
bered that litmus milk does not coagulate as readily or as rapidly as 
plain milk. 
Potato.— New^ potatoes have an acid reaction, as a rule, and old 
potatoes are slightly alkaline. 
Large potatoes are thoroughly scrubbed, the skin removed and 
cut into cylinders with a cork-borer. The cylinders, which should be 
at least 1.5 cm. in diameter, are divided into equal parts by a diagonal 
cut. The pieces are placed in running water over night so that they 
will not darken, and are inserted, base downward, in large test-tubes. 
It is advisable to add about 1 cc. of water to each tube to prevent 
drying. Sterilize in the autoclave. 
1 It should be remembered that ascitic and hydrocele fluids usually contain about 
O.OS per cent glucose. 
