14 
BACTERIOLOGY. 
Func¬ 
tion of 
bacteria 
rain becomes mixed with the soil, the number of bac¬ 
teria present is very large. 
Foods become contaminated with bacteria in a 
variety of ways. Vegetables always have the soil 
bacteria on their surface. Meats if exposed to the 
air take up bacteria from the dust. The surfaces of 
fruits become contaminated with bacteria in the same 
way. In order to diminish the contamination of foods 
as much as possible, ordinances are in force in many 
cities that require meats, fruits, candies, etc., to be 
covered with glass when displayed for sale. 
With bacteria so widely distributed on the earth, 
the question arises as to their use or function in the 
world. We are accustomed to think of bacteria solely 
as the cause of disease, and offhand we would say that 
this was their chief function. This is not true by any 
means, for instead of being harmful to- life they are 
very beneficial; in fact, life could not be maintained 
without them. The causation of disease is a function 
limited to a small group of micro-organisms, and is 
of lesser importance. The much more important use 
of bacteria relates to their ability to produce sub¬ 
stances called ferments or enzymes, which have the 
property of reducing complex organic compounds into 
simpler compounds and chemical elements. 
The plants which form the food of animals would 
soon be exhausted unless they could obtain proper 
nutriment to sustain life and reproduce their kind. 
They live mainly upon carbon and nitrogen in the form 
of nitrates, which would soon be consumed from the 
