CULTURE MEDIA 



55 



acid beef-broth, proceed as follows : Take 1 Ib. of beef 

 (" gravy beef ") free from fat, chop fine or mince, add one 

 litre of tap-water, and allow it to simmer in a saucepan 

 for one hour ; cool, remove any solidified fat from the 

 surface, and filter through filter-paper into a clean glass 

 flask. If not required for immediate use, plug the neck 

 of the flask with cotton-wool, and 

 steam in the steam steriliser (or boil) 

 for three-quarters of an hour on two 

 successive days. It may then be kept 

 until required. 



Peptone beef -broth. Take one litre 

 of the acid beef-broth, add to this 

 10 grm. of peptone (Witte's) and 5 

 grm. of common salt (i.e. 1 per cent, 

 peptone and 0-5 per cent, sodium 

 chloride), mix in a flask, and steam 

 in the steam steriliser until dissolved. 

 When dissolved, remove from the 

 steam steriliser and render slightly 

 alkaline with a 10 per cent, solution 



of caustic soda (preferably) or of 



,. -, 77V, FIG. 8. Tubes of culture 



sodium carbonate , glazed litmus-paper media A Upright agar 

 being used as an indicator. Having B. Potato, c. Sloping 

 done this, return to the steamer for agar> 

 one hour, then filter through two thicknesses of German 

 filter-paper. It should now be quite clear and bright and 

 may be kept in bulk, after sterilising, or be introduced 

 into test-tubes, etc., and sterilised. Beef-broth, if pre- 

 pared in this manner, may need no clarifying, but if it 

 should filter at all cloudy, cool to 50 C., add the white of 

 an egg beaten up with the shell, and steam for half an 

 hour, filter, and finally sterilise as before. Other pre- 

 parations of peptone, e.g. Peptone Chapoteaut, may be 

 used. 



