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63
The milk shall not at any stage be treated by heat.
" Grade A " milk must comply with the following conditions.
The cows must be examined once in every three months by a:
veterinary surgeon. The milk must be delivered in bottles or in
containers of not less capacity than two gallons. A sample of the
milk must not contain more than 200,000 bacteria per cubic centimetre
nor any bacillus coli in one-hundredth of a cubic centimetre.
" Grade A (Tuberculin Tested) " Milk must comply with the
following additional condition. The cows must be tuberculin
tested by a Veterinary Surgeon once in every six months.
'* Pasteurised " Milk must comply with the following condition.
The milk shall be pasteurized, that is to say, retained at a temperature
of not less than 145° and not more than 150° Fahrenheit for at least
half an hour, and be immediately cooled to a temperature of not
more than 55° Fahrenheit.
The milk shall not be so heated more than once and shall
not be otherwise treated by heat. A sample of milk must not
contain more than 30,000 bacteria per cubic centimetre, nor any
bacillus coli in one-tenth of a cubic centimetre.
Although in the summer months, especially, most milk sold
in this district has been heated, from a public health point of view,
the term " pasteurization " should be confined to the process of
heating to not less than 145° F. and not more than 150 F. for a
period of thirty minutes.
When milk is treated in this way, no appreciable change takes
place in the milk proceins. If ordinary raw milk is allowed to
stand, the cream gradually rises to the top and a line of demarcation
appears between the cream and the remainder of the milk. This
layer of cream, sharply demarcated from the rest of the milk, is
known as thp cream line
When milk is pasteurized at 145° F. for thirty minutes, the
cream line is hardly at all affected. The cream line, however, is
affected above this temperature; the cream rises slowly and
imperfectly and in milk pasteurized at 148° F. the cream line may
be decreased by 40 per cent.