228 



BACTERIA 



Hence it has come to be recognised that one of two 

 manipulations must precede such microscopic examination. 

 These simple processes are known by the terms of sediment- 

 ation and centrifugalisation. Sedimentation means merely 

 placing the milk in conical glasses in a cool 

 place for twenty-four hours. The intro- 

 duction of improved forms of the centri- 

 fuge has brought the second method of 

 securing a sediment into preference. Five 

 cubic centimetres of the milk are intro- 

 duced into the graduated bottle, which is 

 then placed in the centrifuge, and whirled 

 for one or two minutes. Thus a deposit 

 of particulate matter is ensured. Cover- 

 glass specimens of the sediment or deposit 

 are then prepared and stained in the ordi- 

 nary way. 



In testing for tubercle something more 

 is generally necessary. To the 50 cc. of 

 the milk set aside for sedimentation 10 cc. 

 of liquefied, colourless carbolic acid are 

 added. The mixture is shaken and poured 

 into the conical glass. After standing for 

 twenty-four hours a little of the sediment 

 is taken by means of a pipette and exam- 

 ined by ordinary methods, though after 

 " fixing " the films with heat they are 

 some times passed through equal parts of 

 alcohol and ether. The stain is of course 

 that usually adopted in tubercle, namely, the Ziehl-Neelsen. 

 Scheurlen suggested a method for demonstrating the tu- 

 bercle bacillus in milk by steeping the cover glasses first in 

 alcohol and then ether, after which they were stained with 

 Ziehl-Neelsen. 



2. Plate Culture. The milk is to be diluted a thousand or 



A CENTRIFUGE 



Used in the Examination 

 of Milk 



