198 MILK AND THE PUBLIC HEALTH chap. 



According to Eevis, " this treatment with Eau de Javelle 

 completely dissolves leucocytes, etc., mixed with the dirt, while 

 without any action on the dirt constituents. We therefore 

 get a true estimation of the dirt, and the procedure quite 

 excludes any loss during manipulation. The dirt, after this 

 treatment, may be used for microscopical examination." 



5. Direct Volumetric Measurement of the Centrifugalised 

 Sediment. — The method of Eevis, while accurate, is complicated 

 and tedious, and the results obtained are not worth the trouble 

 involved. Houston's method and Orr's modification both require 

 a litre of milk, an amount not conveniently available for ordinary 

 control routine work. For scientific investigation Orr's pro- 

 cedure is to be recommended. For routine work a rough but 

 sufficiently reliable estimation of the volume of the sediment 

 may be obtained by direct centrifugalisation. Tubes which 

 are of narrow calibre at the lower closed ends (similar to those 

 used by Orr, Fig. 10) are used, preferably with a capacity 

 of 50 c.c. The milk is filled in to a definite volume (50 c.c.),, 

 centrifugalised for a definite period at a known rate, and the 

 volume of sediment directly read off in the graduated narrow 

 end. The results are doubled and returned as volume of sedi- 

 ment per 100 c.c. of milk. 



It will be convenient to consider in this chapter the value 

 of the cytological and sediment estimations. 



Value of the Cytological Estimation. — In Chapter I. the 

 factors which determine and influence the cellular content of 

 the milk of individual cows are considered in some detail It 

 was there shown that while variations may be met with under 

 different natural conditions, evidence of considerable value is 

 obtainable from this estimation and from a determination of 

 the difierent kinds of cellular elements present. 



The opinion of the writer,^ expressed in 1910 as a result 

 of his personal experience, is that — 



. . . leucocyte enumerations, as far as individual cows are con- 

 cerned, are of great value. Rigid standards as to the number of 

 leucocytes to allow in milk cannot be set up, but the count indicates 

 the need for local investigation. With extended experience it may 

 do much more than this. It gives definite information which 



^ Savage, Journ. Royal Instit. of Public Health, 1910, xviii. p. 65. 



