336 MILK AND THE PUBLIC HEALTH chap. 



It is clear that a certain proportion of these cows are not 

 slaughtered, but are lost sight of under the imperfect powers 

 available. 



(c) Their Influence upon the Purity of the Milk Supply as 

 a whole. — Del(5pine in Manchester has paid careful attention 

 to this indirect but important aspect of the subject. He 

 estimates the amount of dirt in milk by a method which 

 enables comparison between the different years to be instituted. 

 By his scale for the years 1897, 1898, and 1900 over 60 

 per cent of the milk samples examined gave sediments 

 measuring 9 mm. or more. For 1901 the amount fell so 

 that only 40 per cent of the samples gave sediments 9 mm. 

 or more. The amount remained about the same for the 

 following five years, but in 1906a further improvement was 

 noted, only about 32 per cent giving sediment of 9 mm. or 

 more. Delepine ^ gives the following table : 



Amoivnt of Sediment separated hy Gentrifugalisation. 



The numbers indicating the amount of sediment show only the relative 

 amount. The absolute amount of sediment is not given in this table. 



If the amount of sediment be accepted as a reliable 

 measure of the cleanliness of a milk supply these results 

 show that the operation of the Manchester Milk Clauses has 

 resulted in a considerable improvement in the cleanliness of 

 the milk supplied to the city. 



' Mqmrt to the Mcmchcsler Sanitary Committee, 1908. 



