I6O APPENDIX 



neutral to phenolphthalein. Therefore 980 c.c. (i.e. 100020 c.c.) 



will require I x 980) = 117-6 c.c. sodium hydrate solution 



N 

 equal to 1 176 c.c. alkali. 



N 



One c.c. of acid is deducted for each 100 c.c. or TO c.c. for 

 o 



N 

 the litre. Therefore 176 c.c. alkali is actually added to the 



medium and a + ro reaction is obtained. 



If the medium is already alkaline to phenolphthalein, the 

 sample removed for titration should be made acid by the 

 addition of a definite and accurately pipetted amount of 



N N 



H 2 SO 4 . The mixture is then boiled and alkali run in in 



the ordinary way. A simple calculation gives the required 



N 

 result. This is preferable to the direct use of H 2 SO 4 , titrating 



to the neutral point. 



Preparation of Nutrient Media. 



Nutrient Broth (Lemco). Lemco broth is slightly less nutrient 

 than fresh beef broth but is more uniform in quality, cheaper 

 and more readily made. It is suitable for most public health 

 purposes. 



Weigh out 5 grammes Liebig's extract of beef (Lemco) r 

 5 grammes of sodium chloride, and 10 grammes of Witte's 

 peptone, mix with I litre of sterile rain or distilled water in an 

 enamelled saucepan, and boil for a few minutes. Transfer to a 

 flask and make up to one litre again. Steam in current steam 

 for 45 minutes. Estimate the reaction, and bring to a + ro re- 

 action. Filter into a clean flask, and again steam for 30 minutes. 

 If then not perfectly clear filter again. Distribute into clean 

 and preferably sterile test-tubes, about 10 c.c. for each tube, 

 plug with cotton wool, and sterilize in current steam for three 

 successive days for half an hour each day. 



Nutrient Gelatine. Boil up the constituents of broth as above 

 in an enamelled saucepan and transfer to a flask, making up to 



