150 Milk and Its Products 
wholesome product for this particular purpose. The 
expense of producing milk of this particular grade 
is necessarily great, as the labor involved is very 
much more than that required to produce ordinary 
market milk, and the continual oversight by trained 
men unavoidably increases the cost of production very | 
materially. Certified milk differs from pasteurized or 
sterilized milk in this important essential. The 
former is kept as clean and as free from foreign 
matter as possible, while the latter is treated usually 
to some degree of heat, to kill and prevent the 
growth of objectionable bacteria. Perhaps the most 
ideal condition for the consumption of milk is secured 
when the milk is drawn by the young directly from 
the mammary glands of the mother. However, when 
the dairyman attempts to serve his customers in the 
great cities, hundreds of miles from the source of 
production, with a like quality of milk, many difficul- 
ties are encountered, some of which are discussed in 
the following pages. It is the aim of the producer 
of certified milk to approach as nearly as possible 
the ideal condition above mentioned by excluding all 
foreign matter and by keeping the milk at a low 
temperature. 
Certified milk has been kept for months in a per- 
fectly sweet condition. It, has been sent from the 
interior of this continent to Europe, and returned with- 
out any indication of souring. After such a journey 
or length of time, it would not, however, be considered 
as safe for food as the fresh product, even though it 
had not soured to any perceptible degree. 
