36 BACTEEIOLOGY 



inoculation and further cultivation of the micro-organisms 

 depends on the particular kind under observation. 



Preparation of meat bouillon. — The following recipe gives 

 Loffler's method of preparing a liquid medium {broth or 

 bouillon) which has come into general use : — A half-kilogram 

 weight of meat freed from fat is chopped fine in a mincing 

 machine. (Such meat cannot, strictly speaking, be termed 

 free from fat, because only the masses of fat are cleared 

 away, whereas that which exists in the substance of all 

 meat is not removed.) A litre of ordinary water is poured 

 over the meat and the whole is allowed to stand in a cool 

 place for twenty-four hours. In this way the albuminoid 

 bodies and other substances soluble in water are dissolved 

 out from the meat, the result being an aqueous extract, 

 coloured in most cases with hsemoglobin, and which is 

 separated from the residue by squeezing it through a cloth. 

 About a litre of fluid is thus obtained, which must now be 

 freed from albuminoid bodies by heating in a water-bath or 

 in the steam-steriliser. The heating must be kept up until 

 a sample, when filtered and boiled, no longer shows any 

 turbidity, which usually takes about half an hour. The 

 fluid is then filtered, and to the filtrate are added one per 

 cent, of dry colourless peptone and 0'5 per cent, common 

 salt, which is equivalent to 10 grams peptone and 5 grams 

 salt to the litre of water. After this the solution is boiled, 

 and, as it has a feebly acid reaction, is neutralised with a 

 saturated solution of sodium carbonate, until it causes 

 in litmus paper a slight blue coloration, which afterwards 

 passes into a faint red. It is not essential to add water to 

 make up what has been lost through evaporation, but it 

 will do no harm to do so if desired. The broth thus prepared 

 is boiled once more and filtered after boiling ; it should 

 not become turbid; either during sterilisation or on standing. 

 The filtrate must be clear, pale yellow, and of neutral 



