124 



BIOLOGY AND TECHNIQUE 



most frequently employed in this way, should be left in this position 

 for two or three days. (See Fig. 21, b.) 



ACTUAL STEPS IN THE PREPARATION OF NUTRIENT MEDIA 



Broth.— Meaf Extract Broth.— 1. To 1,000 c.c. of distilled or clear 

 tap water add 5 gms. Liebig's meat extract, 10 gms. Witte's pepton, 



and 5 gms. common salt (NaCl). 



2. Weigh solution with containing 

 vessel (any suitable agate-ware vessel 

 or glass flask will do). 



3. Heat over free flame until thor- 

 oughly dissolved, stirring constantly. 



4. Weigh again and make up loss 

 by evaporation. 



5. Determine volume. 



6. Titrate and adjust to required 

 reaction, heating over free flame foi 

 five minutes. 



7. Filter through paper until clear 



8. Sterilize. 

 If medium can not be cleared by 



filtering through paper, clearing by 

 white of egg may be resorted to and 

 the medium filtered through cotton. 



Meat Infusion Broth. — 1. Infuse 

 500 gms.' of lean meat, twelve to 

 twenty-four hours, with 1,000 c.c. of 

 distilled water in refrigerator. 



2. Strain through wet cotton flan- 

 nel or wet cheese-cloth and make up 

 volume to 1,000 c.c. 



3. Add 5 gms. common salt and 

 10 gms. Witte's pepton. 



4. Weigh with containing vessel. 



5. Warm over flame or water bath, stirring until pepton is dissolved, 

 not allowing temperature to rise above 50° C. 



6. Determine volume. 



Fig. 26. — Maassbn Filter, for 

 SMALL Quantities of Fluid. 



' Roughly, 1 pound (IJ lb.). 



