MILK HYGIENE 113 



cubic centimeters of the milk are centrifugalized for twenty 

 minutes at a speed of 2000 revolutions per minute. The 

 supernatant liquid is removed by a fine-pointed glass tube 

 attached to an aspirating pump by means of a rubber tube. 

 The cream adhering to the sides of the tube is removed by 

 the use of absorbent cotton. Smears are prepared from the 

 sediment, dried, fixed, and stained as follows: The preparation 

 is flooded with carbol-fuchsin and heated over a water bath 

 or by passing through the flame of a Bunsen burner until the 

 preparation steams. Allow the hot dye to act three to four 

 minutes, and then wash. Decolorize with a 5 per cent solu- 

 tion of nitric acid in 80 per cent alcohol until the red color 

 is discharged. Wash and stain with aqueous methylene blue 

 for a minute. Tubercle bacilli appear as slender red rods on 

 a blue field. 



Experience should be gained in the demonstration of 

 tubercle bacilli by the staining and examination of prep- 

 arations from sputa. The student should bear in mind that 

 the tubercle organism in sputum is longer and more slender 

 than in milk. In sputum it also has a distinct tendency to 

 form a " beaded " appearance. 



In manure, and in dust from hay and fodder, there are fre- 

 quently found organisms, the so-called "acid-fast" bacteria, 

 which possess the same relation to decolorizing agents as the 

 tubercle bacillus. Many of these are very similar in morphol- 

 ogy to the tubercle bacillus, differing, however, in cultural 

 characters and in pathogenicity. Through the contamination 

 of the milk with manure and barn dust this type of bacteria 

 is likely to find its way into the milk, and care must be exer- 

 cised in the examination of milk sediments not to mistake 

 such forms for true tubercle bacilli. A strict differentiation 

 in such cases can only be made by 'animal inoculation. 



