39 2 AGRICULTURAL BACTERIOLOGY. 



CHAPTER XVII. 



DISINFECTION. 



BACTERIA are both useful and detrimental. Taking to- 

 gether the facts mentioned in the previous pages it is evident 

 that their usefulness outweighs the injury they do. Still it is 

 clear that they sometimes occur where they are not wanted 

 and produce mischief. It becomes, therefore, a matter of espe- 

 cial importance to the farmer, not only to learn how to stimu- 

 late the growth of the friendly species, but how to check the 

 growth of the hostile forms, and if possible how to destroy them 

 entirely. A brief consideration of the methods of disinfection, 

 adopted under various conditions, is necessary before closing 

 our consideration of bacteria in relation to agriculture. 



The purpose of all kinds of disinfection is to treat material 

 infested with bacteria in such a way as either to destroy the 

 bacteria present, or to prevent their further active growth. 

 These two objects are, however, somewhat different from each 

 other. Manifestly the prevention of active growth is more 

 easily accomplished than the actual destruction of bacteria. 

 By the term germicide is meant some substance or method of 

 treatment which actually kills all bacteria, while the term an- 

 tiseptic refers to what will check their growth, and thus de- 

 stroy their power to do injury, although not actually killing 

 them. Nearly all agents which will act as germicides when 

 applied in large quantity, will act simply as antiseptics when 

 used in lesser quantity. We look therefore for antiseptics 

 and germicides along similar lines. 



In considering how we may guard against the injurious 

 action of bacteria which may have infested our houses, barns, 



