394 General Botany 



H2O, and nitrogen are delayed by the formation of rather stable 

 intermediate products. These form the humus of soils. 



Some of the bacteria of decay are of importance in industrial 

 processes, as in the retting of flax and hemp fibers and in the prep- 

 aration of hides for the making of leather. 



Spontaneous generation and bacteriology. Not many years 

 ago it was thought, even by the most learned persons, that the 

 minute plants and animals that occur in stagnant water and that 

 cause decay and fermentation arose spontaneously in the water. 

 It was the experiments of Pasteur (1862) and Tyndall (1869) that 

 finally proved that the organisms get into liquid media from the 

 air. It was these studies that led to the discovery of the relation 

 between bacteria and disease. The experiments of Lister (i860) 

 led to the use of antiseptics (Latin : anti, against, and septicus, 

 putrid) in surgery. Modern methods of sanitation, the control 

 of diseases, and antiseptic surgery have all been developed since 

 i860. It is quite impossible for us to realize to what extent the 

 dangers to life have been removed through the development of 

 the science of bacteriology. This science has also made it possible 

 to make use of bacteria in many important industries. 



Methods of killing and controlling bacteria. Long before the 

 discovery of the importance of bacteria, many methods of pre- 

 serving foods, of caring for wounds, and of avoiding disease 

 had been tried. They were very crude when compared with 

 those that have been perfected since bacteria have been carefully 

 studied. In the following table some of the methods of control 

 are listed, and opposite them are a few domestic and industrial 

 applications. Can you add to the list ? 



1. Cleanliness Washing, keeping down dust, certified milk, 



disposal of garbage, sewage disposal 



2. Ventilation Sleeping porches, open-air schools 



3. Sunlight Purification of water supplies 



4. Drying Hay, fruits, vegetables, milk, eggs, pem- 



mican 



