PREPARATION OF CULTURE MEDIA. 285 



carbonate. Next sterilise the fluid in the autoclave at 115 C. 

 for fifteen minutes, and then filter through moistened " Chardin" 

 paper. Place in tubes or a sterile flask and again sterilise at 

 115 C. for half an hour. 



Nutrient Gelatine. To broth prepared as above add 15 per 

 cent. " gold label " gelatine, and place in the steam steriliser 

 until all the gelatine is dissolved. Then make faintly alkaline 

 with the sodium carbonate solution, cool to 50 C., and add the 

 white of an egg dissolved in 50 c.c. of distilled water. Boil for 

 an hour or until the fluid is clear, and then filter through 

 moistened " Chard in " paper placed in a hot-water filter. 

 Divide the filtrate into sterile tubes, 10 c.c. in each, and sterilise 

 in the steam steriliser at 100 C. on three successive- days for 

 half an hour each day. 



Agar-Agar. Broth prepared as above is placed in a flask 

 and rendered distinctly alkaline. Two per cent, of agar power 

 is then added to the alkaline fluid ; if agar is added to an 

 acid medium it is converted into galactose. The flask is heated 

 in the steam steriliser until the agar is dissolved ; the contents 

 are then cooled to 50 C., and the white of an egg dissolved in 

 50 c.c of distilled water added. The flask is now heated in 

 the autoclave at 115 C. for three-quarters of an hour, and the 

 contents are then filtered through moistened " Chardin " paper 

 placed in a hot-water funnel. The filtrate is divided amongst 

 sterile test-tubes, 7 c.c. in each, which are then sterilised in 

 the autoclave at 115 C. for half an hour. 



Glucose-broth, glucose-gelatine , and glucose- agar are made by 

 adding 2 per cent, of glucose to each of the media prepared as 

 above, but before sterilisation has been effected. Sugar media 

 should not be sterilised at a temperature above 100 C. 



Cane-sugar-gelatine and lactose-gelatine are prepared in the 

 same manner as the glucose media. 



Peptone Solution. Witters peptone, 1 percent., and common 

 salt 0*5 per cent., are dissolved in water with the aid of 

 heat (as a rule the fluid does not require the addition of an 

 alkali, the peptone being sufficiently alkaline). The mixture 

 is then boiled, filtered, and divided amongst sterile tubes, 

 which are then sterilised in the autoclave at 115 C. for twenty 

 minutes. 



