SUMMARY 
317 
helpful ones; and (2) harmful ones cannot do their work, or 
even live, in a perfectly healthy body, for such a body is 
constantly preparing a substance (antitoxin) which neu¬ 
tralizes the bacterial poison (toxin). Our chief aim, then, 
should be to keep well, and a few simple rules of hygiene will 
accomplish this. (1) Spend as much time as possible exer¬ 
cising in the open air. (2) Sleep as many as eight hours out 
of twenty-four in a well-ventilated room or out of doors. 
(3) Eat only food which agrees with you, and not too much 
of that. (4) Wear seasonable clothing. (5) Keep the skin 
clean through frequent bathing. (6) Have a definite occupa¬ 
tion, work faithfully at it, do your best, and don’t worry. 
SUMMARY 
The smallest and simplest of all the plants are the bacteria. 
Most of them are helpful, ridding the earth of waste material, 
giving flavor to food, gathering nitrogen from the air for 
plants, and aiding in the making of linen and sponges. Some 
bacteria are harmful and cause diseases in plants and animals. 
Bacteria are spherical, spiral, or rod-shaped. They are 
found everywhere, unless special pains have been taken to 
remove them. If they have plenty of food, air, moisture, 
and warmth, they multiply rapidly, and they go into the 
resting state, in which they can remain for a long time if 
any or all of the necessary conditions of growth are lacking. 
The harmful bacteria during their growth secrete a poisonous 
substance, toxin. When there are enough bacteria present 
to make a large quantity of toxin, the animal or plant host 
is made ill. Some bacteria, especially in the resting state, 
can bear freezing or boiling without being killed. In order 
to make anything “keep,” it is necessary either to kill all the 
bacteria by making the substance sterile or aseptic, or to put 
into it a preservative, a substance in which the bacteria 
cannot grow. We should use great care to avoid the bac¬ 
teria known to produce disease. 
