108 PRINCIPLES OF BACTERIOLOGY 
(c) Neutralize the acidity if in excess of 1.5 per cent. 
(d) Add a few drops of a 5 per cent aqueous solution 
of litmus. 
(e) Sterilize in Arnold’s sterilizer for thirty minutes 
on three successive days. 
11. Loeffler’s Serum Medium 
Loeffler’s serum medium is used for diphtheria bacil¬ 
lus. 
(a) Beef blood is collected in sterilized jars, allowed 
to clot, the clot is loosened by a glass rod, and jars are 
kept on ice overnight. 
(b) Clear serum is pipetted off to sterile flasks. 
(c) To three parts of the serum one part of 1 
per cent glucose meat infusion broth is added, and the 
whole is tubed. 
(d) It is then sterilized in a special sterilizer called 
“ inspissator ” at a temperature of 70° C. for two hours 
on six successive days. 
12. Endo’s Medium 
Endo’s medium is used for the differentiation of the 
typhoid and colon bacilli. 
1. Prepare ordinary meat extract agar, except that it 
should contain 25 to 30 grams of agar per 1,000 c.c. of 
media, except the usual 15 grams, and it should be 0.2 
per cent acid. Do not tube it, but keep it in flasks. When 
Endo’s medium is wanted, melt the agar, add to it 1.8 
c. c. of filtered 10 per cent solution of basic fuchsin in 95 
per cent alcohol and 25 c.c. of freshly prepared 10 per 
cent aqueous solution of sodium sulphite crystals. Then 
add 10 grams of lactose (milk sugar) in 50 c.c. of sterile 
water. Sterilize for fifteen minutes in Arnold’s sterilizer 
on three successive days. 
