ENUMERATION OF CELLS 745 



for twenty minutes at 1,500 revolutions per minute, and the 

 upper fluid is pipetted or syphoned off. Some of the sediment 

 should be examined with the -in. and |-in. objectives for the 

 presence of " dirt," e.g. hairs, straw, etc. Three smear prepara- 

 tions 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. 741), considerable caution 

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

 cocci present are not necessarily pathogenic, as non-pathogenic 

 lactic-acid-forming streptococci are common. For counting the 

 number of cells present, Kevis l 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 2,000 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 

 of the narrow end down to within in. of the deposit are sucked 

 out with a fine glass pipette, the upper part of the tube is wiped 

 clean, and the tube is then filled to the 10-c.c. mark with salt 

 solution. The tube, having been violently shaken till all the 

 deposit is distributed through the liquid, is then rotated for four 

 minutes, and the liquid down to within |- in. of the deposit again 

 removed. In the case of small deposits, two to three drops of 

 saturated aqueous solution of methylene-blue are added, and the 

 deposit is stirred up by blowing through a fine glass capillary 



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



