Ad MEDIA AND THEIR PREPARATION 
isms. The reaction should be determined with phenolphthalein since 
this has been adopted as the standard indicator. Five cubic centi- 
meters of the media should be titrated and brought to the desired 
reaction means of standard NaOH or HCl. 
Recent work, however, indicates that this method does not yield 
satisfactory results. Clark and Lubs (1917) have pointed out that 
the hydrogen ion concentration must be determined more accurately 
either by means of the hydrogen electrode or special indicators. The 
former technique is too long and complicated to be applied to the 
preparation of ordinary media and it is probable that indicators will 
have to be used. These are mentioned in the appendix under indicators. 
BoviLtton Mepia 
Nutrient Broth. This medium is used as a base to which the other 
constituents of media may be added. The following procedure for its 
preparation is recommended by the Laboratory Committee of the Ameri- 
can Public Health Association in Standard Methods for the Examina- 
tion of Water and Sewage, 1917, p. 95. 
1. Add 3 gms. of meat extract and 5 gms. of peptone to a liter of 
distilled water. 
2. Heat slowly on the steam bath to at least 65° C. 
3. Make up lost weight, titrate, and if the reaction is not already 
between +0.5 and +1 adjust to +1. 
4, Cool to 25° C. and filter * through paper until clear. 
5. Distribute in test tubes about 10 c.c. in each tube. 
6. Sterilize in the autoclave at 15 lbs. pressure (120° C.) for fifteen 
minutes after the pressure reaches 15 lbs. 
Carbohydrate Broths. These are made by adding to plain broth, 
as prepared above, 1 per cent of the sugar desired just before steriliza- 
tion. No attempts are necessary to remove muscle sugar since the 
constituents of broth are free from fermentable sugar. The reaction 
of carbohydrate broth may be neutral to phenolphthalein or adjusted 
to neutrality according to Standard Methods, 1917. Mudge (1917) 
has shown that during sterilization maltose and lactose are broken 
down and that sucrose and raffinose are not. The Arnold steam 
sterilizer was found to cause more hydrolysis than the autoclave. 
*The Sharples laboratory centrifuge is in use at the University of Illinois for 
the clearing of solid media. It gives satisfactory results and obviates the use of cot- 
ton and egg albumin. It is considered a valuable addition to the laboratory equip- 
ment. 
