196 Culture Media and Bacteria Cultivation 



After titration the bouillon must again be boiled for a few 

 minutes, in order to precipitate the acid albumins, as much 

 water added as has been lost by evaporation, and the fluid 

 filtered through a pharmaceutic filter. 



The filtered fluid is dispensed in previously sterilized tubes 

 with cotton plugs about 10 c.c. to each or in flasks, and 

 is then sterilized by steam three successive days for fifteen 

 to twenty minutes each, according to the directions already 

 given for intermittent sterilization, or superheated in the 

 autoclave. 



The loss of water during boiling is an important matter 

 to bear in mind, as unless properly replaced it is the cause 

 of disproportion between the fluids and solids of the media. 

 The quantity must therefore be measured before filtration 

 and enough water added to replace what has been lost. 

 Measuring before filtration is comparatively easy with 

 bouillon, but difficult with heavy liquids, like the gelatin 

 and agar-agar solutions. To overcome this difficulty it is 

 best to make the entire preparation by weight and not by 

 volume. A pair of platform scales with sliding indicators 

 will first balance the empty kettle and then show the correct 

 quantity of each added ingredient. After boiling, the kettle 

 can be returned to the scale and the exact quantity of water 

 to be added determined. 



II. To Prepare Bouillon from Meat Extract. When 

 desirable, the bouillon may also be prepared from beef- 

 extract, the method being very simple: To 1000 c.c. of 

 clean water 10 grams of Witte's dried beef-peptone, 5 

 grams of sodium chlorid, and about 2 grams of beef-extract 

 are added. The solution is boiled until the constituents 

 are dissolved, titrated, and filtered when cold. If it be 

 filtered while hot, there is always a subsequent precipitation 

 of meat-salts, which clouds it. 



Bouillon and other liquid culture media are best dis- 

 pensed and kept in small receptacles test-tubes or flasks 

 in order that a single contaminating organism, should it 

 enter, may not spoil the entire quantity. A very convenient, 

 simple apparatus used by bacteriologists for filling tubes 

 with liquid media is shown in figure 34. It consists of a 

 funnel to which a short glass pipet is attached by a bit of 

 rubber tubing. A pinch-cock, at b, controls the outflow of 

 the liquid. The apparatus need not be sterilized before 



