32 LIQUID MEDIA 



1. Into each test-tube put 10-15 c.c. of broth, and into each flask 25 c.c. 

 A small glass funnel should be utilized for distributing the broth, because 



if a drop of it come in contact with the wool plug it will when dry cause the 

 wool to stick to the mouth of the tube, so that the plug can only be removed 

 with difficulty. (The use of a funnel is even more important when solid 

 media, such as agar or gelatin, are being tubed.) 



2. Plug the tubes and flasks with wool. 



3. Place the vessels containing the medium in a wire basket, and auto- 

 clave for 20 minutes at 110-115 C., taking care that the latter tempera- 

 ture is not exceeded, and that the precautions noted in Chapter I. are 

 observed. 1 2 



Veal broth. 



For the preparation of veal broth proceed as for beef broth, using instead 

 of beef 500 grams of lean veal. 



Chicken broth. 



Chicken broth is prepared in a similar manner, using 500 grams of chicken 

 meat. All skin, tendon, and bone must be removed, otherwise the broth 

 will be of a gelatinous consistency. 



Giblet broth. 



Liver, spleen, etc., may be used for making broth. The technique is the 

 same as in the preceding cases, substituting 500 grams of the solid organs 

 for beef or other meat. Very often these broths exhibit a slight cloudiness, 

 but this cannot be avoided. 



Meat extract. 



1. To 500 grams of well-minced lean beef or veal, add 1000 grams of water, 

 and leave in the ice chest to macerate for 12 hours. 



2. Shake the mixture, filter through a cloth and squeeze all the fluid out 

 of the meat, then filter through a Chardin paper. 



3. Add 5 grams of salt to the filtrate, and heat to boiling, 



4. Neutralize as in the case of peptone beef broth. 



5. Autoclave for 5 minutes at 115 117 C. 



6. While warm, filter through a moistened Chardin filter paper. 



7. Add sufficient distilled water to make up the volume to a litre. 



8. Distribute in tubes and sterilize at 110-115 C. 



Martin's peptone solution. 



Pigs' stomach broth. 



1. Wash, clean and mince finely 4 or 5 pigs' stomachs. 



It is better to use a number (5) of stomachs in order to neutralize variations in 

 their pepsin content ; if this be done, the broths will have an almost constant 

 average composition. 



2. Mix the following : 



Minced stomachs, - - - 200 grams. 



Hydrochloric acid (pure), ..... 10 ,, 



Water at 50 C., - - 1000 



and keep the mixture at a temperature of 50 C. for 20-24 hours. 



1 Sometimes it will be noticed that the medium when taken out of the autoclave is 

 very slightly cloud} 7 ; this will vanish on cooling. But if during sterilization the tem- 

 perature exceed the temperature of the first autoclaving (par. 6, above), the broth remains 

 permanently cloudy. 



[ 2 In England it is more usual to sterilize media by steaming for 20 minutes on each 

 of three successive days in a Koch's steamer, or some suitable modification of it (Chap. I.).} 



