2(5 
HOUSEHOLD BACTERIOLOGY . 
Effect of 
Sunlight 
Power of 
Movement 
live much longer when grown in a cellar than when 
cultivated in the light rooms of a house. 
All disease germs, so far as known, are killed by 
direct sunlight. This was proved some years ago 
by planting a Petri dish with typhoid fever germs. 
Half of the dish was covered with black paper, while 
the uncovered half was exposed to direct sunlight. 
On the sunlighted half no growth appeared, while 
the other half showed many colonies. A similar ex¬ 
periment is illustrated by Fig. 15. 
In this experiment the letters of the name “Ty¬ 
phus” were cut out of black paper and placed on the 
under side of the cover of a Petri dish which had 
been planted with bacteria. The dish was exposed 
to sunlight for an hour and a half and then left in a 
dark room for twenty-four hours. When the paper 
letters were removed, the space covered by them was 
found thickly studded with the minute colonies of 
bacteria. The rest of the plate showed no appearance 
of bacterial life. 
Some bacteria, like most of the higher plants, re¬ 
main stationary, having no power of motion, while 
others move by slow or jerky, worm-like contrac¬ 
tions. Still others are moved about by whip-like ex¬ 
tensions of their bodies, called flagella or* cilia. Some 
have only one whip at one end of the body, others 
one or a cluster at each end, while others have them 
reaching out from all parts. Fig. 16. 
Some bacteriologists place all the forms which have 
