182 CELLS, DIRT AND DEBRIS 



rod valve, the lower tube is detached, the contents rejected and, 

 after reconnecting with the lower tube, 50 c.cms. of distilled 

 water are added and the valve withdrawn. After stirring the 

 sediment thoroughly with a platinum needle, the tube and 

 contents are given a further five minutes in the centrifuge. The 

 supernatant liquid is removed as before but prior to the final 

 washing with distilled water, the sediment is treated with 1 

 c.cm. of Eau de Javelle (antiformin may be substituted) for 

 the purpose of dissolving the leucocytes and epithelial cells. 

 After the final washing, the valve is inserted, and the lower 

 cap removed and dried in the water oven with its contents. 

 From the weight so obtained the tare of the cap is deducted 

 and a correction made for a blank determination on the mate- 

 rials used. The dirt may be used for a microscopical examina- 

 tion. According to Revis, the hypochlorite has no action on 

 dirt constituents, but in view of the well-known action of chlo- 

 rine on cellulose this statement must be accepted with reserve. 



Group 2. The filtration methods included in this group 

 are practically all based on the filtration of a given volume of 

 milk through a disc of cotton wool followed by an inspection of 

 the disc for visible dirt. 



Tonneyi^ suggested the use of a small disc of absorbent 

 cotton in a Gooch crucible and operated with reduced pressure 

 obtained from a water pump. This is a fairly satisfactory pro- 

 cedure for laboratory examinations but is usually precluded by 

 an insufficiency of sample. This principle of filtration for the 

 purpose of demonstrating visible dirt has led to the manufacture 

 of many commercial types of apparatus which have been used in 

 dairies and creameries, and by milk inspectors, with more or less 

 success. The types now on the market are the Lorenz or Wis- 

 consin, Stewart, and Gerber, which use gravity filtration, and 

 the Lorenz improved and Wizard which employ pressure or 

 suction. A detailed account of these has been given by 

 Schroeder ^^ of the Health Department of New York City, 

 but as these are of but very limited utility in laboratory work 

 they will not be discussed ** in extenso " here. 



