21.5,  the  difference  between  3.5  and  25,  is  the
number  of  pounds  of  30  per  cent,  cream  needed ;
and  5,  the  difference  between  30  and  25,  is  the  num-
ber of  pounds  of  3.5  per  cent,  milk  needed.  There-
fore, any  given  amount  should  be  mixed  in  the
proportion  of  5  parts  milk  to  21.5  parts  cream.
MARKET  MILK

The  essentials. — The  rapidity  with  which  milk
deteriorates  and  the  impossibility  of  really  making  it
perfect  after  it  has  been  neglected,  especially  when
it  is  remembered  that  much  of  the  milk  shipped  does
not  reach  the  consumer  until  it  is  36  to  48  hours
old,  make  it  imperative  that  milk  should  have  the
right  care  from  the  start.  The  essential  features
for  good  market  milk  are  that  it  shall  be  from
healthy  cows,  fed  on  feeds  free  from  strong  odors
and  flavors.  Dust  and  manure,  especially,  with
their  accompanying  load  of  bacteria,  should  be  kept
out  of  the  milk,  and  it  should  be  immediately  cooled


62


FIRST   LESSONS   IN   DAIRYING


to  a  temperature  below  50°  to  retard  the  growth  of
those  bacteria  which  gain  access  in  spite  of  the  pre-
cautions taken.  The  whole  story  briefly  is:  keep
the  milk  clean  and  cold.
