126 INTERRELATIONS OF PLANTS AND ANIMALS 



3. Place No. 2 in direct sunlight as much as possible. 

 (Keep it moderately cool.) Results as before ? 



4. Place No. 3 uncovered but in a very dry place for a few 

 days. Results ? 



Conclusions. 1. What effect have dark warm places on the 

 growth of bacteria ? 



2. What effect has sunlight on the growth of bacteria ? 

 Lack of moisture ? 



3. What conditions favor the growth of bacteria ? 



4. What are some of the conditions that retard or hinder 

 the growth of bacteria ? 



5. What causes food to spoil ? 



6. Name some of the various ways of preserving food. Ex- 

 plain just why they may be successful. 



b. Some Relations to Man 



1. PUTREFACTION OR DECAY 



Materials. Hay infusion, beef juice, microscope, slides, 

 charts or figures of bacteria. 



Observations. 1. Make a hay infusion by pouring some hot 

 water on some chopped-up hay in a quart jar, and allowing to 

 stand a day or so in a warm place. What changes in color do 

 you observe ? Note. There must have been some germs on 

 the hay that developed as soon as it was warm and moist 

 enough. These germs must have survived the hot water, and 

 after it was the right temperature, developed rapidly, feeding 

 on the infusion from the hay. 



2. Prepare some beef juice and set it aside in a warm place, 

 in a beaker. After a day or so note any changes in color and 

 odor. 



3. Examine a drop from each of the preparations with at 

 least a J-inch objective, use a higher power if possible. Do 

 you see any signs of life ? Compare them with Figure 36. 



Conclusions. 1. What do you think caused the hay and the 

 beef juice to change their color and odor (decay or putrefy)? 



