3 6 AIDS TO BACTERIOLOGY 



well mixed, and raised and maintained at the boiling- 

 point for ten minutes. The precipitated albumin is then 

 filtered off, and the filtrate sterilised as above directed. 



Stitt uses 3 grammes of Lemco to the litre, and, as the 

 msdium has almost invariably a reaction of +0'75 (Ameri- 

 can scale), considers it is usually unnecessary to titrate 

 and adjust the reaction unless precision is demanded. 



Glycerin Broth. Five c.c. of glycerin to every 100 c.c. 

 of beef broth. 



Glucose and Lactose Broth. To each 100 c.c. of broth 

 is added 1 to 2 grammes of pure glucose or lactose. Used 

 in the cultivation of anaerobic bacteria. 



Nutrient Gelatin. To 1 litre of acid beef broth are 

 added 100 grammas of ' gold label ' gelatin, 10 grammes 

 of peptone, and 5 grammes of salt. The mixture is 

 placed on a water-bath until solution is complete, and 

 then rendered faintly alkaline to litmus-paper with 

 sodium hydrate solution. -After cooling to 50 C., the 

 white of an egg is added, and after stirring it is steamed 

 for one hour. The gelatin is now filtered through a 

 pleated filter in a hot- water funnel, and then run into 

 test-tubes. The tubes are sterilised on three successive 

 days in the steam steriliser for fifteen minutes on each 

 occasion. After the final steaming they are allowed 

 to solidify in upright or slanting positions, according as to 

 whether they are intended for stab or streak cultivations. 

 In hot weather 15 or 20 per cent, gelatin should be used. 

 The gelatinising power of gelatin is gradually destroyed 

 by heating. 



Glucose Gelatin. Two per cent, of glucose in nutrient 

 gelatin. 



Nutrient Agar. Fifteen grammes of powdered agar are 

 well boiled with a litre of nutrient broth for two to three 

 hours until dissolved; the water lost by evaporation is 

 replaced from time to time. Care is then taken to see 

 that the medium is faintly alkaline, after which it is 

 cleared with egg-albumin, as described under the prepara- 

 tion of gelatin. The agar is then filtered through ' Char- 

 din ' filter-paper or a small jelly- bag. Some workers 

 allow the hot agar to stand in the steam steriliser in a tall, 

 cylindrical vessel till the flaky particles which cause the 

 turbidity sink to the bottom, when the clear agar can be 

 poured off. 



