428 APi'LIED BACTERIOLOGY 



only diminished to a slight extent ; secondly, the taste and 

 smell of the milk are not permanently altered ; thirdly, less 

 carbon dioxide is driven off; fourthly, the condition of the 

 fat remains practically unchanged ; fifthly, the lact-albumin 

 is not coagulated. 



Tyrotoxicon in Milk. — The presence and detection of this 

 poisonous ptomainic body in milk and milk products has 

 already been dealt with (see p. 118). 



Examination of Milk for the Tubercle Bacillus. — This can 

 be best done by Van Ketel's method, as follows : To 50 c.c. 

 of the suspected milk add 10 c.c. of liquefied colourless 

 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. 140). 



Scheurlen's method for demonstrating the tubercle 

 bacillus in milk is to steep it for twenty-four hours in 

 absolute alcohol, digest in ether for another twenty- four 

 hours in order to remove the fat, and stain according to 

 Ziehl's method. Ilkavitch {Munchener med. Wochenschr., 

 1892, p. 5) described a convenient method of applying this 

 result : 20 c.c. of milk are coagulated with citric acid, 

 filtered and dissolved in saturated aqueous solution of 

 NagPO^. The solution is treated with 6 c.c. of ether, the 

 fat which rises to the surface is decanted, and the re- 

 mainder, after the addition of one or two drops of acetic 

 acid, is centrifugalized in a copper tube with a screwed 



