TUBERCULOSIS 325 



Growth in artificial media is always slow, and fortunately little 

 or no growth occurs in milk. 



Glycerin Agar. Bs. tuberculosis grows scantily or not at all 

 on ordinary agar or gelatine. On glycerine agar the growth in 

 ten to twelve days is small and crumbly ; later it extends, and 

 in six or eight weeks may form a wrinkled lichen-like patch, 

 whitish-yellow or brownish-yellow in colour. 



Potato. It grows in four or five weeks on potato placed in 

 a Roux's tube and kept moist with five per cent, glycerine ; the 

 growth is dull and yellowish. 



Veal broth containing 5 or 6 per cent, of glycerine is a good 

 medium for it. Small cream-coloured flocculent masses are 

 produced in the liquid with surface film-formation occasionally. 



Ex. 150. Examine a sample of milk for "acid-fast" organisms. 



(a) Half fill two centrifuge tubes with milk and rotate for five 

 minutes at 2000 revolutions per minute. 



(b) Break up the cream and centrifuge again. 



(c} Remove the cream and pipette off the milk to just above 

 the deposit. Add water so as to half fill the tubes and rotate 

 for five minutes. 



(d) Pipette off the water, and transfer a drop of the liquid and 

 the deposit with a platinum loop to a cover-slip. When air-dry 

 pass through flame. 



(<?) Determine if any " acid-fast " bacteria are present. To do 

 this take the cover-slip and place upon it 2 or 3 drops of weak 

 carbol-fuchsin (see Ex. 8). Gently heat to steaming - point 

 (60 C.) over flame for three minutes with aid of Cornet forceps, 

 adding fresh stain to supply the place of that which evaporates. 

 If preferred, the films may be heated while staining over an 

 asbestos board or copper plate, or floated in a watch-glass 

 containing the stain. 



(/) Wash well in water and then immerse in a 25 per cent, 

 solution of sulphuric acid for twenty seconds : wash in water, 

 and if pink colour comes out repeat the treatment with acid and 



