34 LIQUID MEDIA 



4. Boil for 5 minutes. Filter. Add sufficient water to make the volume 

 up to a litre. 



5. Distribute in tubes. Sterilize at 115 C. 



Liebig's broth. 



1. Dissolve 5 grams of Liebig's extract of meat [" Lemco "] in 1000 grams 

 of water, warming gently. Neutralize if necessary. 



2. Autoclave for 5 minutes at 115-117 C. Filter through a moistened 

 paper in the warm. 



3. Distribute in tubes. Sterilize at 110-115 C. 



Peptone (Chapoteaut) (10 grams) and salt (5 grams) may be added to the medium 

 before neutralization. 



In the same way a nutrient broth may be prepared with Cibils' extract. 

 In that case 20 grams of the extract is used instead of the Liebig. 



These media are used chiefly in German laboratories, [and the former to a large 

 extent also in England]. 



Thymus broth (Brieger). 



1. Obtain the thymus from two or three calves directly after they are 

 slaughtered. Mince the glands finely and add an equal weight of distilled water. 



Mix, and macerate for 12 hours. 



2. Filter through muslin and squeeze out as much of the fluid as possible. 

 Add an equal volume of water to the cloudy viscous filtrate. 



3. Make feebly alkaline with a 10 per cent, solution of sodium carbonate. 



4. Heat to 100 C. for 15 minutes in the autoclave or steamer (a higher 

 temperature interferes with the properties of the medium). 



Filter through a piece of fine linen. 



5. Distribute in sterile tubes. 



Sterilize at 100 C. for 15 minutes on each of two successive days. 



Some micro-organisms, such as the cholera vibrio, will only grow satisfactorily 

 on this medium provided that 5 or 6 times its volume of sterile water be added 

 just before use. 



Serum broth. Blood broth. 



These media are prepared by adding to tubes of ordinary sterile broth, 

 one-half, one-third or one-quarter their volume of blood-serum, ascitic 

 fluid, or blood collected under aseptic precautions (p. 45 and Chap. XII.). 



Achalme, in the preparation of blood broth, advises the use of a 1 per 

 cent, solution of commercial haemoglobin instead of blood. The haemoglobin 

 must first be sterilized by filtration through a Kitasato's filter (p. 25). 



The preparation of these media will be more fully considered when dealing 

 with the Gonococcus and Pfeiffer's bacillus. 



On account of the difficulty of obtaining sterile blood, Bernstein and Epstein 

 recommend the following procedure for the preparation of blood broth: collect 

 400 c.c. of ox blood in a flask containing 30 c.c. of a 1 per cent, solution of ammonium 

 oxalate in distilled water and 0*5 c.c. of formalin ; shake, and in half an hour 

 dilute the mixture with 3 volumes of normal saline solution. After standing for a day 

 or two at the temperature of the laboratory, distribute in agar or broth in the pro- 

 portion of 1 part to 15 of medium. The formalin is thus so highly diluted that it 

 does not interfere with the growth of micro-organisms. The Pneumococcus, Gono- 

 coccus and Meningococcus all grow very well in this medium. 



Carbohydrate broths. 



These media are prepared by adding to beef broth, at the "same time as 

 the peptone and salt, 2-4 per cent, of one or other of the following carbo- 

 hydrates : glucose, saccharose, lactose, galactose, mannite, dulcite, maltose, 

 Isevulose ; the preparation is completed as in the case of broth. 



