304 



LIVES OF PLANTS AND ANIMALS 



bacteria of 

 decay are, 

 presents 



hay is infused 

 i«:to N/ccter- 



break dovn 

 thehqx 



it for a few days in a warm room, certain changes are seen to j 

 take place in the contents of the jar ; the water after a little 

 while gets cloudy and darker in color, and a scum appears on the 

 surface. If some of this scum is examined under the compound 

 microscope, it will be found to consist almost entirely of bacteria. 

 These bacteria evidently aid in the decay which (as the un- 

 pleasant odor from the jar testifies) is taking place. As we have 

 learned, bacteria flourish wherever the food supply is abundant. 



The bacteria them- 

 selves release this 

 food from the hay by 

 causing it to decay. 

 After a few days 

 small one-celled ani- 

 mals appear which 

 multiply with won- 

 derful rapidity. Hay 

 is dried grass, upon 

 which the wind may 

 have scattered some 

 of these little organ- 

 isms in the dust from 

 dried-up pools. Ex- 

 isting in a dormant 

 state on the hay, 

 they are awakened 

 by the water to active 

 life. In the water, 

 too, there may have been some other living cells, plant and 

 animal. 



At first the multiplication of the tiny animals within the hay 

 infusion is extremely rapid ; there is food in abundance and near 

 at hand. After a few days more, however, several kinds of one-; 

 celled animals may appear, some of which prey upon others.! 

 Consequently a struggle for life begins, which becomes more and| 

 more intense as the food from the hay is used up. Eventually! 

 the end comes for all animals unless some green plants obtain a 



water evaporates 

 animals form 

 spores on 

 Yuxy 



tiny animals 



arise from 

 spor-ds 



larger animals appear 

 and. use the 

 foodt 



The development of life in a hay infusion. How can you 

 account for the bacteria that attacked the hay ? 



