CHAPTER X 



BACTERIA AND SANITATION 



Experiment i. Yeast Plants. — With a microscope examine a drop 

 from a glass of water in which you have washed grapes or apples 

 (Fig. 129). 



Experiment 2. Fermentation. — Put a tablespoonful of sugar into 

 this water and set the glass in a warm place for a day or two. Do 



you see any bubbles of gas ? 

 Have the odor and taste 

 changed ? Does the micro- 

 scope show that the yeast 

 plants are now more abun- 

 dant ? By fermentation, or 

 the growth of yeast in sugar, 

 sugar is changed into carbon 

 dioxid, a gas, and alcohol, a 

 liquid. 



Experiment 3. A Sani- 

 tary Map. — Construct a 

 sanitary map of the com- 

 munity. Indicate houses 

 where consumption, typhoid 

 fever, or other transmissible 

 diseases have occurred, with 

 number of cases. Mark loca- 

 tion of stagnant waters where 

 mosquitoes breed, mark 

 garbage dumps, unclean streets. Suggest where improvements may 

 be made in drainage, dust, noises, sunshine, shade, etc. 



Bacteria, or microbes, the smallest living things, are 

 visible only under a microscope of high power. (See 

 "Plant Biology," p. 182.) They obtain food either from 

 dead tissue or from degenerate tissue of living plants and 



158 



Fig. 129. — Yeast Cells magnified 200 

 diameters, or 40,000 areas). Yeast plants 

 multiply by budding. Notice small cells 

 growing on larger and older ones. 



