SPECIAL MEDIA 47 



Neutralise with caustic soda until the reaction is distinctly alka- 

 line, filter into test tubes, and sterilise in the autoclave at 1 10' for 

 ten minutes, allowing the tubes, during sterilisation, to lie on a bed 

 of cotton-wool in order to prevent the alkaline solution of lactose 

 turning brown through too sudden heating. 



31. Extract of malt — 



Thoroughly crush 100 grammes of freshly malted barley, and 

 place in a litre of water. Shake well and allow to macerate for 

 one hour. Place in a water bath and raise the temperature very 

 slowly to from 50° to 55°. Maintain it at this for one hour, care 

 being taken not to exceed a temperature of 58° or the diastase 

 transforming the starch into maltose will be destroyed. At the 

 expiration of the hour bring up quickly to boiling point, filter 

 through Chardin paper, run into tubes, and sterilise in the Koch 

 at 100' for half an hour on three successive days. 



12. Gelatinised beer-wort — 



Take i litre of fresh beer-wort (preferably un-hopped). 

 Sterilise in the autoclave at 115' for twenty minutes, and allow 

 to stand for a fortnight. Decant, filter, heat up to 80', add 100 

 grammes of best gelatine, stirring well. Clarify and filter as in 

 the case of ordinary nutrient gelatine, run into test tubes, and 

 .steam in the Koch steriliser for half an hour at 100^ on three 

 successive days. If a liquid medium is desired omit the gelatine 

 and heat up to 60^ only before the addition of the white of &^g. 

 Steam in the Koch to ensure good coagulation and proceed as above. 



33. Peptone solution {DunJiani) — 



Make into a paste of the consistency of thick cream by the 

 addition of a little distilled water 10 grammes of dry peptone 

 (Chapoteaut or Witte), and 5 grammes of sodium chloride. Add 

 slowly I litre of boiling water, stirring well. Boil for five minutes, 

 stirring constantly. Filter, and run into test tubes. Sterilise in 

 the autoclave for fifteen minutes. Owing to the natural alkalinity 

 of the dry peptone this medium rarely requires neutralisation. 

 Used for indol reaction. 



34. Hay infusion — 



Cut into small pieces 1 5 grammes of hay, and allow to macerate 

 in I litre of water for three hours. Bring slowly to boiling point, 

 and allow to boil for five minutes. Filter, test reaction, and 

 neutralise, acidify, or make alkaline, as desired. Steam in Koch's 



