S8 THE BACTERIOLOGICAL EXAMINATION OF MILK 



allow to stand for twenty-four hours. Filter three times and place 

 in a drop bottle, of a deep amber colour preferably, 



Lofflers Alkaline Blue. 



Methylene-blue, saturated alcoholic solution . . -30 c.c. 



Caustic potash, -01 per cent, aqueous solution . , loo c,c. 



Shake well and filter. Should be used fresh, as staining power 

 weakens with age. 



Saturatea Alcohol Solutions of Methylene-blue or Gentian Violet. 

 Colouring matter . . . . . i part. 



Absolute alcohol . . . . .10 parts. 



Shake the above well together, and allow to stand for twenty- 

 four hours, shake again, allow to settle, and filter twice, and again 



Fig. 6. — Conical glass. Fig. 7. — Simple holder for stain filtration. 



finally into a drop bottle of colour as above. These solutions will 

 keep for a long time if not exposed to strong light. 



Dilute aqueous solutions of the above are used in the stain- 

 ing of all ordinary bacteria. The solutions are made by adding 

 to every 10 cubic centimetres of distilled water from two to five 

 drops of the concentrated solution. In the case of Ziehl-Neelsen 

 or other carbol stain the appearance on the surface of the liquid 

 of a bronze iridescence will indicate that a proper strength for the 

 dilute solution has been reached. The dilute stains should be 

 prepared only when required for use, and a convenient form of 

 conical glass for this purpose, as well as for many others in the 

 general work of the laboratory, is shown on Fig, 6. The glass used 

 should be marked on the outside, with a diamond or a fine file 

 dipped in turpentine, at the level of 5, 10, 15, and 20 c.c. of water. 

 In use it is filled to the required level with distilled water and the 



