256 CITY MILK SUPPLY 



so rushed that it fails in its object. A device that will insure the cans 

 being exposed to the steam for a measured interval of time is needed. 



Dirt in Milk. The amount of dirt that is found in milk varies a great 

 deal according to whether a small-top milk pail is used in milking and 

 other sensible precautions to keep the dirt out are taken. Some figures 

 that have been published show that the dried sediment in the milk of 

 seven German cities varied from 3.8 to 13.5 mg. per liter; in Copenhagen, 

 Denmark, the milk contained from 1 to 13 mg. ; in certain Norwegian 

 cities the sediment averaged 2.6 mg.: in Washington, D. C., some samples 

 contained as high as 180 mg. In American cities the amount of visible 

 dirt in milk, even as it is delivered to the consumer, is often very great 

 as any one can tell for himself by gently lifting the bottle and examining 

 the bottom. Evans at one time estimated that the citizens of Chicago 

 receive 25 tons of dirt per year in their milk. 



Clarification of Milk. The cream separator is often used to clarify 

 milk. As the milk passes through the machine practically all of the in- 

 soluble dirt, some casein, cellular debris from the udder and bacteria 

 collect as a slime on the wall of the separator bowl. The separated cream 

 and skim-milk are recombined by mixing them. In many instances the 

 process has given satisfaction, in others it has not. In passing through 

 the separator the clusters of fat globules are broken up and to some extent 

 the globules themselves are disrupted. Consequently, the recombined 

 milk does not show as sharp a cream line as the untreated milk which often 

 leads customers to complain. The bacterial clumps and chains are 

 broken by the passage of the milk through the separator so that the 

 recombined milk and cream has a higher bacterial count than the un- 

 separated milk. This process has been thought to injure the keeping 

 qualities of the milk and the explanation therefor has been given that 

 as individuals the bacteria multiply more rapidly than in aggregates. 

 Such an explanation is theoretical and it has not been a universal experi- 

 ence that the clarified milk fails to keep. 



Specially constructed machines called clarifiers have come into gen- 

 eral use in large milk plants for removing the visible dirt from milk; be- 

 sides this they abstract mineral salts, casein, cells from the udder and 

 bacteria. The machines depend on the centrifugal principle but the 

 cream is not separated in passing through them; hence the clarified milk 

 creams normally. It has been claimed that in clarifying by these ma- 

 chines a notable removal of cells and bacteria is effected and that the milk 

 is greatly improved thereby. Others are of the belief that the numbers 

 of bacteria in the milk are increased by breaking up the clumps and chains 

 of the organisms and that the keeping quality of the milk is impaired. 

 It is the author's opinion that while these clarifiers always remove large 

 numbers of bacteria and cells their effect on the bacterial content of the 

 milk is not uniform, the numbers being sometimes increased, and other 



