HOUSEHOLD BACTERIOLOGY 55 



The soil used was a kind of beef-broth jelly. The seed was ordinary 

 dust from an ordinary room. The boxes had been baked for over an 

 hour in a very hot oven. The jelly had been steamed a number of times, 

 until no living thing could possibly be therein. 



A dust garden planted after a room had been carefully swept is shown 

 in Fig. 25. When the cover of the box was removed and the dust raised 

 by the broom into the air had settled on the soft, sticky jelly, something 

 happened! In about twenty-four hours little specks appeared, which 

 rapidly or slowly grew larger and developed various colors. Unfortunately, 

 the photograph does not show the delicate greens, yellows, and blues of 

 the different spots. As they grew larger some spots revealed a feathery 

 or velvety surface and, like that at the left side, a dark center with dust 

 flying from it. The other spots were shiny, wet, or waxy in appearance, 

 and never showed any increase in height or any dark, dusty center. 



Every housewife who has seen mold on her bread or on her jelly, in 

 her pickle jar, or possibly on shoes and books, will suspect that the velvety, 

 dark-centered spots are of similar nature. Molds spread their cells over 

 the food, sending some cells down into the substance and others upward. 

 From the tops of the upright cells grow others, and in or on them are formed 

 thousands of dust-like specks, called spores. Each of these spores may 

 start a new bed of mold. The infinitely tiny spores falling on soft sub- 

 stances, such as cheese or bread, send invisible lacy threads down into 

 the substances; while on books, leather, wood, or cloth they may grow 

 only over the surface and may remain invisible. 



Certain spots in the dust garden are colonies of bacteria. Each 

 spot shows where one plant or cell touched the jelly. This cell fed, and 

 divided itself in the middle. These two cells repeated the process, until 

 perhaps there were a hundred or more. Then a tiny speck became visible. 

 No one ever saw, with the naked eye, a single bacterium or a mold spore. 



In Fig. 26 is shown a dust garden with soil exactly like that of the one 

 shown in Fig. 25, but the dust that planted it was thrown into the air 



by using a feather duster. 



' 



KINDS OF PLANT MICRO-ORGANISMS 



Dust plants are micro-organisms. There are large numbers of minute 

 organisms so small that they cannot be seen by the naked eye but require 

 the aid of a powerful microscope to show their presence; hence their 

 name, " micro-organisms." Various names have been given to these 

 minute living bodies, such as " germs " and " microbes." Literally, 

 germ means the beginning, the first living cell that produces a more com- 

 plex form. 



The plant micro-organisms that we shall consider are bacteria, molds, 

 and yeasts. 



