EXAMINATION OF MILK 619 



If a diphtheroid organism is detected it must be isolated and 

 examined by culture tests and animal inoculation. 



In milk and cheese a bacillus is frequently met with closely resembling 

 the diphtheria bacillus in its morphological and cultural characters , 

 it is, however, quite non-pathogenic. 1 



3. The typhoid, paratyphoid, Gartner, and dysentery bacilli 

 and cholera vibrio may be searched for by the methods given for 

 " Water." 



(4) The M. pyogenes and the Streptococcus pyogenes may be 

 searched for by means of plate cultures on glycerin agar. 



(5) Examination of sediment. Houston and Savage (loc. cit.) 

 have devised methods for the quantitative estimation of the sedi- 

 ment by centrifuging in special graduated tubes. For the micro- 

 scopical examination of the sediment the milk is centrifuged 

 for twenty minutes at 1500 revolutions per minute, and the upper 

 fluid is pipetted or syphoned off. Some of the sediment should be 

 examined with the f in. and in. objectives for the presence of 

 " dirt," e.g. hairs, straw, etc. Three smear preparations are then 

 made, each with four drops of the sediment, which are spread evenly 

 over three-fourths of the slide. The slides are air-dried, and may 

 be treated with a mixture of absolute alcohol and ether for ten 

 minutes. One slide is stained with Loffler's blue, another by 

 Gram's method for streptococci, and a third by the tubercle method. 

 The Loffler's blue specimen gives a general idea of the number of 

 bacteria present, and of the presence of cells. 



From what has been said above (p. 616), considerable caution 

 must be exercised in stating the presence of pus-cells. Streptococci 

 present are not necessarily pathogenic, as non-pathogenic lactic- 

 acid-forming streptococci are common. For counting the number 

 of cells present, Revis 2 employs a centrifuge tube of 10 c.c. capacity, 

 the lower third of which is contracted to 0-8 cm. in diameter, and 

 contains 1 c.c. The procedure is as follows : 



In the tube are placed 5 c.c. of the well-mixed milk, diluted to 

 the 10 c.c. mark with 0-8 per cent, salt solution. After inserting 

 a rubber stopper the contents are well mixed. The tube is then 

 centrifuged at about 2000 revolutions per minute for two minutes, 

 the cream is broken up by violently shaking the upper part of the 

 tube, and the rotation continued for four minutes longer. A glass 

 rod, fitting roughly the narrow neck of the tube, is inserted, and 

 the major part of the milk poured off, and the upper part of the 

 tube well rinsed with water to remove cream, etc. ; the contents 



1 See Scientific Bull. No. 2, Health Dept., City of New York, 1895, p. 10. 



2 Journ. of Hygiene, vol. x, 1910, p. 58. 



