tutes the greatest difficulty in modern
dairy practice, owing to the liability of the milk to absorb bacteria,
which during transit may multiply enormously.

The multiplying of bacteria in milk at different temperatures is easily
demonstrated, and the result of this has been stated in various forms
many times over. As a graphic means, however, of showing the increase
that takes place in the numbers of germs present, and the consequent
product of acidity, the table below by Conn may be given.

The consequent result of the increase in bacteria is the production of
lactic acid, which produces the souring so familiar in milk which has
been kept in the household at a high temperature.

_Numbers of Bacteria per c.cm. in Milk kept at
Different Temperatures._

--------------------------------------------------------------------------
Number In 12 In 12 In 50 In 50 hrs. or at No. hrs. No. hrs.
at hrs. at hrs. at hrs. at time of curdling to curdle to curdle
Outset 50deg.F. 70deg.F. 50deg.F. at 70deg.F. at 50deg.F. at 70deg.F.
--------------------------------------------------------------------------
46,000 39,000 249,500 1,500,000 542,000,000 190 56
47,000 44,800 360,000 127,500 792,000,000.36 hrs. 289 36
50,000 35,000 800,000 160,000 2,560,000,000.42 hrs. 172 42
--------------------------------------------------------------------------

What actually happens is that the lactic acid is produced by the
breaking up of the milk sugar, and the appearance of this sourness is an
indication that a period has been reached in the age of the milk which
may be described as being--unwholesome.[46]

It is necessary, therefore, for the town's milk dairy to be equipped in
such a way as to deal promptly with the milk supply.

We have seen that the milk should first of all be aerated at blood heat,
so as to liberate objectionable odours, after which it should be cooled
to as low a temperature as possible, by means of well water. When these
operations have been performed on the farm, milk should be sent as
rapidly as possible to the distributing towns' dairies, and should be
transported in refrigerated waggons, cooled preferably with ice, during
the journey. On arrival at the town dairy, it will be necessary to
pasteurise the milk--that is to say, the milk should be heated to such a
temperature as will destroy any pathogenic organisms