1320 Wisconsin Academy of Sciences, Arts, and Letters. 
as well as the presence of the casein, that was thought to be a 
desirable innovation. It is prepared as follows: 
10 grams of peptone and 3 grams of extract of beef are 
added to 1 liter of water. When the peptone and beef extract 
have gone into solution, as a result of gentle heating, 500 c. c. of 
separated (i. e., fat-free) milk are added, and the reaction of the 
whole is then so adjusted as to bring the reaction to +0.7. Fif¬ 
teen cubic centimeters of a 1 % aqueous solution of neutral red 
is added. The medium is then ready to be put into fermentation 
tubes and sterilized as other sugar media. 
Fig. 7. Gasometer for Durham tubes. 
In such a medium B. coli first coagulates the casein, then turns 
the medium in the closed arm yellow, forms gas, and also by its 
reducing action causes the whey or fluid part of the medium to 
become fluorescent. The amount of gas formed by B. coli in this 
medium is considerably less than that produced in lactose pep¬ 
tone bile, i. e., from 12 to 35% as contrasted with from 30 to 
70%. In addition to this there are the changes in the milk part 
of the medium as well as the changes in the neutral sred. The 
advantages of this medium over the lactose peptone bile are first, 
the ease with which it is prepared, since the materials are prac¬ 
tically always at hand in all laboratories, and second, the large 
