PLANTS WITHOUT CHLOROPHYLL 



143 



presence of bacteria in our own environment. They are evidently 

 present in the air, and in greater quantity in air that is moving 

 than quiet air. Why? 

 That they stick to par- 

 ticles of dust can be 

 proven by placing a 

 little dust from the 

 schoolroom in a culture 

 dish. Bacteria are pres- 

 ent in greater numbers 

 where crowds of people 

 live and move, the air 

 from dusty streets of a 

 populous city contains 

 many more bacteria 

 than does the air of a 

 village street. The air 

 of a city park contains 

 relatively few bacteria 

 as compared with the 

 near-by street. The air 

 of the woods or high 

 mountains fewer still. 

 Why ? Our previous 

 experiment has shown 

 that dirt on our hands, 

 the mouth and teeth, 

 decayed meat and vege- 

 tables, dirty money, the 

 very hairs of our head are 

 all carriers of bacteria. 



Fluids the Favorite Home of Bacteria. — Tap water, stand- 

 ing water, milk, vinegar, wine, cider all can be proven to con- 

 tain bacteria by experiments similar to those quoted above. 

 Spring or artesian well water would have very few, if any, 

 bacteria, while the same quantity of river water, if it held any 

 sewage, might contain untold millions of these little organisms. 







figure to show the relative size and shape of 

 (1) a black mold, (2) yeast cells, and (3) dififer- 

 ent forms of bacteria ; B, bacillus ; C, coccus ; 

 S, spirillum forms. The yeast and bacteria are 

 drawn to scale, they are much enlarged in pro- 

 portion to the black mold, being actually much 

 smaller than the mold spores seen at the top of 

 the picture. 



