328 APPLIED BACTERIOLOGY 



carbolic acid. The mixture is well shaken for a few minutes, 

 and poured into a conical test-glass to settle for twenty- four 

 hours. A little of the deepest layer of the sediment is then 

 removed with a fine pipette, from which cover-glass prepara- 

 tions are prepared as usual, by rubbing a droplet between 

 two perfectly clean cover-glasses. The films are then air- 

 dried and ' fixed ' by passing through the flame three times. 

 The cover-glasses are then passed through a mixture of equal 

 parts of alcohol and ether. The cover-glasses are now dried 

 and stained by the Ziehl-Neelsen method, as described under 

 ' The Staining of the Bacilli in Sputum ' (p. 124). 



When a sample is required to be examined at once, the 

 milk can be ' whirled ' in a centrifugal machine, and the 

 sediment taken for examination as above. This method ' 

 could probably be improved by the addition of alcohol to the 

 milk to reduce its viscosity, thereby facilitating the separa- 

 tion of the organisms. 



Examination for the Typhoid Bacillus. — The milk can be 

 examined by one of the methods described under ' The 

 Examination of Water.' 



Determination of the Number of Organisms. — The numerical 

 determination of the bacteria present in milk can be de- 

 termined by the method already described under ' The 

 Examination of Water,' except that the dilution, owing to 

 the much larger number of organisms present, requires to 

 be carried to a much greater extent. If the samples cannot 

 be plate-cultured at once, they should be allowed to remain 

 in an ice-safe, otherwise the results, owing to the rapid multi- 

 plication of the bacteria, will have but little practical value. 



