216 BACTERIOLOGY 



times through the flame, moistened with a few drops of 

 dilute aqueous solution of methyl violet, and examined at 

 once under the microscope. The tubercle bacilli, if present 

 in the preparation, remain completely colourless if the 

 examination is not protracted beyond five or ten minutes, 

 whereas all the other bacteria almost instantly assume a 

 blue colour. 



In very doubtful cases in which the ordinary methods 

 of staining are at fault, preparations must be made from 

 the sediment. According to Stroschein's method, a table- 

 spoonful of sputum is vigorously shaken in a test-glass with 

 three tablespoonfuls of a mixture of 1 part concentrated 

 solution of boric acid and 3 parts water until the sputum 

 is liquefied, when it is poured into a glass ending in a point 

 below. After standing for twenty-four hours, the clear 

 supernatant liquid is poured off and a cover-glass prepara- 

 tion made from the sediment at the bottom. 



Biedert recommends that a tablespocnful of sputum 

 should be boiled with two tablespoonfuls of water and seven 

 or eight of solution of caustic potash ; four more table- 

 spoonfuls of water are then added, and boiling is repeated 

 until the mass has become evenly fluid. This remains 

 standing for three or four days in a pointed glass covered 

 over, and is then poured off until a depth of only five to 

 eight millimeters is left. The sediment is energetically 

 stirred up with some fresh white of egg, and some of the 

 mixture is rubbed on a cover-glass, dried at a moderate 

 heat, and stained by the Ziehl-Neelsen method. A small 

 quantity of untreated sputum from the same source may 

 be used instead of the white of egg for fixing the sediment 

 to the cover -glass. 



Sedimentation is particularly important in the examina- 

 tion of fluids which are poor in corpuscular elements, and is 

 most conveniently done by centrifuging. In the absence, 



