STUDIES OF SPORE-PLANTS 285 



(/) Chemicals. Many chemicals kill bacteria, and are 

 called germicides or disinfectants. Some chemicals when 

 much diluted do not kill bacteria, but prevent their multi- 

 plication. Such are called antiseptics. Corrosive sublimate 

 (mercuric chloride), and carbolic acid are two powerful 

 germicides, killing bacteria even when much diluted. Most 

 strong acids and alkalies are also germicides. Chloride of 

 lime and washing powders are two efficient germicides for 

 general household cleaning. Among gases, sulphur gas from 

 burning sulphur and formaldehyde from evaporated formalin 

 are now regarded as most powerful germicides. The forma- 

 lin is better because it does not bleach colored articles, is not 

 so poisonous to human lungs, and is easily evaporated in a 

 room either by a special lamp or by the heat generated by a 

 bucket of slaking lime on which the formalin is quickly 

 poured before closing the door of the room. By exposing 

 cultures of bacteria in such rooms, it has been shown that 

 the bacteria are killed by the gas generated. Among common 

 antiseptics are very dilute solutions of formalin, carbolic 

 acid, boric acid, common salt, and many substances pro- 

 duced by plants (menthol, thymol, eucalyptol, camphor, 

 cloves, cinnamon, etc.). The preservative action on foods 

 of common salt, vinegar, creosote (on smoked meats), and 

 spices is due to the antiseptic power of these substances. 

 The more powerful preservatives, such as boric acid, so- 

 dium benzoate, formalin, and salicylic acid are sometimes 

 used in foods ; but there is danger of injuring the digestive 

 organs by amounts so small that the sense of taste does not 

 guard against them. There is no such danger with vinegar 

 and common salt. 



257. Where Bacteria are Found. They may be said to 

 be almost ubiquitous. They are abundant in soils ; water of 

 seas, rivers, and lakes ; in the bodies of animals and plants ; 

 in all dead organic matter in nature ; and in the air (except 

 on high mountains, in polar regions, and in uninhabited desert 



