CHAPTER II 



PREPARATION OF CULTURE MEDIA 



At the present time a large variety of culture media are 

 in use, but for general routine laboratory work the list 

 may be curtailed to five — i.e., (1) broth; (2) agar-agar; 

 (3) gelatin ; (4) blood-serum ; (5) potato. These, except 

 potato, can be purchased already prepared in tabloid form, 

 but for economic reasons they should be prepared in one's 

 own laboratory. 



Broth. 



This is easily prepared, and it forms the basis for the 

 majority of other media. 



Method. — Take 500 c.c. of water, boil well for half an 

 hour in a double-contained saucepan, add 5 grammes Lemco, 

 10 grammes peptone, and 5 grammes of common salt ; 

 then boil for thirty minutes. Now test with litmus-paper, 

 and it will in all probability be slightly acid, in which case 

 a solution of soda should be added drop by drop until the 

 reaction is slightly alkaline. If too much alkali is used, 

 a little hydrochloric acid (diluted), to re-acidify, should be 

 added, and then again neutralize. Now add sufficient 

 water (some having been lost in evaporation) to make up 

 1 litre, and filter through a double thickness of filter-paper 

 into a 500 c.c. flask. 



Dry the mouth of the flask thoroughly to keep the 

 cotton-wool from sticking, and plug firmly with absorbent 

 wool. Sterilize at 60° C. for half an hour for three suc- 

 cessive days. 



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