498 
PREVENTION OF DISEASE 
of a well-cooled refrigerator does not destroy the germs, but 
makes them incapable of growth until heat is supplied them. 
If food is taken from the refrigerator and allowed to stand 
for a time, the bacteria will at once begin to grow and cause 
the food to spoil. If such food is eaten, an intestinal dis¬ 
turbance usually results. 
In the attempts to prevent disease, more study has been 
given to milk and water than to other necessities. For 
discussion of milk, see pages 313-315. 
While milk is used as a food by all mankind, water is 
even more important, for it is absolutely necessary if we 
are to continue to live. 
In this respect man is like 
all plants and all other 
animalis, water being 
necessary for the preser¬ 
vation of all life. 
Two conditions must be 
met before a water supply 
can be deemed satisfac¬ 
tory. There must be an 
abundant supply; but 
more important still, the 
water must be pure, that 
is, free from disease-pro¬ 
ducing germs. Farmers 
and residents of small towns may without great trouble secure 
sufficient pure water, but the large cities have to spend 
millions of dollars in providing an adequate water supply. 
Sanitary measures are adopted to keep the sources of 
the water from becoming impure, as well as to keep clean 
the reservoir where it is stored. Certain harmless plants 
and animals living in reservoirs may give an unpleasant 
taste or odor to the water. Harmful disease germs live 
in water for months. Such germs may be frozen in ice, 
Figure 426. — Milk Diluted to 
Left-hand culture from clean milk; 
right-hand culture from dirty milk. 
Count the number of spots in each 
plate and multiply by 1000 and you will 
have some idea of the difference be¬ 
tween clean and dirty milk. Certified 
milk is almost free from bacteria. 
