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 



