XI EXAMINATION OF MILK 197 



tubing. The centrifuge tube is graduated in x^ths and 3-00^^^ 

 of a c.c. A litre of milk (after addition of 1 c.c. formalin) is 

 allowed to stand for 12 hours. At the end of that time, 

 a brass rod fitted with a rubber stopper at the lower end is 

 passed through the milk, and fitting into the outlet of the 

 cylinder prevents escape of the fluid when the centrifuge tube 

 is detached. The tube is centrifugalised (1500 to 2000 

 revolutions per minute) for 3 to 5 minutes, and the milk 

 poured off. Sodium carbonate solution (1 per cent) is then 

 added up to the 10 c.c. mark and the centrifugalising repeated. 

 The deposit is then read off. The primary reading of Houston 

 is omitted. 



4. Bevis's Method} — A tube holding about 70 c.c. is used. 

 This is made of stout glass drawn out at one end and with 

 a small glass cap well ground on. Inside the neck of the 

 tube upon which the cap fits, a glass rod is well ground in, of 

 sufficient length to project beyond the mouth of the tube. 

 The end of the rod is ground flush with the neck, and the cap 

 has such a capacity that when in place -g- inch in depth is left 

 beyond the end of the tube. It is used as follows : 5 c.c. 

 of milk are placed in the tube, the cap being in place and the 

 rod withdrawn. A rubber stopper is put in, and the tube 

 rotated at about 2000 revolutions per minute for 5 minutes. 

 (The cap should be well backed up with a pad of cotton-wool 

 to prevent breakage.) The rod is then carefully inserted in 

 the tube, the cap gently removed with a screwing motion. If 

 stuck, it may be tapped off with a piece of wood and the tube 

 thoroughly washed out. The cap is replaced, and 50 c.c. of 

 distilled water run in, the sediment stirred up with a platinum 

 needle, and the tube, after well shaking, again rotated for 5 

 minutes. The cap and contents are again removed as before, 

 the tube emptied, the cap replaced, and 1 c.c. of Eau de Javelle 

 run in on to the sediment. This is mixed up with a platinum 

 needle, and the tube again filled up with 5 c.c. distilled water, 

 shaken, and again rotated. The cap is finally removed, dried 

 in the water-oven, and weighed. The cap is then cleaned out, 

 dried, and weighed also. The difference equals the amount of 

 dirt by weight in 5 c.c. of milk after subtracting the weight 

 of a blank Eau de Javelle experiment with distilled water. 



' Journ. Boyal InstihUe of Public Health, 1908, vol. Ivi. p. 734. 



