CHAPTER XXIII. 



PROCESSES OF DECAY. 



(AN AUTUMN OR WINTER STUDY.) 



THE decay and disappearance of vegetation in the 

 autumn, as well as the death of many forms of animal life, 

 suggests an inquiry into the agencies at work in the dis- 

 integration of organic bodies. 



Our first question to our pupils in introducing this 

 subject might well be, What becomes of the leaves which 

 fall from the trees in autumn ? The answer is, they decay 

 in course of time. What is decay ? In terms which our 

 pupils will understand we say it is the breaking up of the 

 substances which at one time formed part of a living body 

 into simpler substances until out of them ordinary con- 

 stituents of soil and air are formed, viz. carbonic acid, 

 water, and ammonia. And the work of decay is carried 

 out by microscopic plants known as bacteria, aided to 

 a small extent by larger plants, the moulds, toadstools, 

 and mushrooms (Fig. 157). 



We cannot see the bacteria, but we may very easily 

 demonstrate their effects. We perform the following 

 experiment. 



Experiment. Take two small thin glass flasks, into 

 which place some organic stuff, e.g. fruit juice, or chopped - 

 up autumn leaves. To both add a little water. If fruit 

 juice is used the demonstration will be made more effective 



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