278 



PROCESSES OF DECAY. 



by filtering the juice free from all sediment. Label the 

 flasks A and B, and note the date of the experiment. 



Take flask A and boil the contents for some time. 

 While the flask is boiling prepare from clean sterilised 

 cotton wool (supplied by the chemist) a small plug with 

 which to stopper the flask. When the liquid is boiling 

 and while the steam is issuing from the flask, insert the 



plug of cotton wool, 

 screwing it in tightly. 

 Flask B, which contains 

 the same substance as A, 

 is to remain open. Set 

 the flasks aside and com- 

 pare the contents from 

 time to time. 



If the experiment is 

 properly performed, the 

 substance in A will re- 

 main perfectly fresh for 

 years, whilst that in B 

 will decompose owing to 

 the presence of bacteria 

 and the spores of moulds, 

 etc. By boiling, all bac- 

 teria adhering to the in- 

 side of the jar, or present 

 in the water or in the 

 organic substances, are 

 destroyed, and the cotton 

 wool acts as a filter, keep- 

 ing those outside from 



getting in. The spores of some bacteria are not readily 

 killed, and sometimes it is desirable to repeat the boiling 

 after a few days, but usually in an experiment of this 

 kind one boiling gives convincing proof that the agents 

 of decay have been destroyed. 



Following this demonstration it is appropriate to refer 

 to the widespread occurrence of bacteria, some of which 

 enter the bodies of living human beings and animals, 

 causing disease, and to the necessity o fresh air in 



MYCELIUM 



Fig. 157. Mycelium and spore-producing 

 branch of a common mould (Eurotium). 



