fact should be kept clearly in mind.)

2. They are microscopic in size and hence the more difficult to deal
with.

3. They are found everywhere that there is life--in the air, in water,
in the soil.

4. They multiply very rapidly under favourable conditions.

5. Some bacteria are useful to the housekeeper; many kinds are her
enemies.

6. Some of these enemies get into food and, growing there, cause a
change in it--then we say the food is spoiled.

CONDITIONS OF BACTERIAL GROWTH

All plants have the same requirements. Any well-known plant may be put
before the class to help them to think of these. They must be told that
microscopic plants differ from other plants in one respect; they do not
need light. Hence bacterial requirements are as follows: (1) water, (2)
food, (3) air (oxygen), (4) heat.

The class should be led to see that if any one of these conditions is
removed, the remaining ones are insufficient for the plant's activity.

MEANS OF OVERCOMING BACTERIA

To the housekeeper, preserving food means overcoming bacteria. There are
only two ways of doing this, either of which may be chosen:

1. Kill the bacteria in the food and exclude others.

2. Subject the food to conditions which are unfavourable for bacterial
growth.

In the first way, extreme heat is used to kill the bacteria in the food,
and then while hot, the food is sealed to keep out other bacteria:
Example, canning.

In the second way, conditions are made unfavourable to the bacteria in
the food, as follows:

1. The bacteria are deprived of water; the food is dried.

2. The bacteria are deprived of sufficient heat to be active; cold
storage is used.

3. Large quantities of certain substances which are detrimental to the
growth of bacteria are put into the food, and the bacteria become
inactive. Examples: salt, sugar, spices, vinegar, smoke, or certain
chemicals.

When the lesson is finished, the class is ready to practise the
principles it involves. The lessons on the special preservation of fruit
may follow at once.

[Illustration: Utensils used in canning]

CANNING

As canning is the method of preservation most commonly used, practice
should be given in this method. In rural schools with a limited
equipment, it may be that only one jar can be prepared. In other
schools, it may be impossible to provide each pupil with material for
work, on account of the expense. In the latter case, the materials may
all be brought fro