To Prepare Bouillon from Meat Extract 229 



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 45. It consists of a 

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

 rubber tubing. A pinch-cock, at 6, controls the outflow of 

 the liquid. The apparatus need not be sterilized before 

 using, as the culture medium must subsequently be sterilized 

 either by the intermittent method or in the autoclave after 

 the tubes are filled. The test-tubes and flasks into which 

 the culture medium is filled must, however, be previously 

 sterilized by dry heat, unless the subsequent sterilization 

 is to be performed in the autoclave, when it may be un- 

 necessary. 



