60 THE CORNELL READING-COURSES 



principle involved, and had unknowingly availed herself of the assistance 

 of the invisible plants. 



The action of bacteria is very useful in the production of linen, jute, 

 and hemp, in the tanning of leather, and in the maceration of skeletons. 

 The destruction of garbage by means of the septic tank is owing to a certain 

 class of bacteria. 



METHODS OF DESTROYING THE EFFECTS OF BACTERIA 



Heat 



All bacteria are promptly killed by heat unless they are in the spore 

 form or the resting stage. There are resting stages of some of these 

 organisms when the conditions for active life are unfavorable. The 

 organism itself may dry up and assume a dormant form, resuming its 

 active form when favorable conditions recur; or it may throw off spores. 

 Spores resist heat far better than does the active or vegetative organism ; 

 so, although we may have used enough heat to kill the active forms, we 

 cannot be sure that we have destroyed all organisms unless we know that 

 the particular organism which we seek to exterminate does not form spores 

 or is not in the spore stage. Boiling for twenty minutes will generally, 

 but not always, kill most forms of bacteria, including the spores. Water 

 is pronounced safe when it is thus boiled. Mere simmering of water is 

 not sufficient. 



Fresh air and sunshine 



Direct sunshine kills most bacteria. Many persons are afraid to take 

 fresh air and sunshine in sufficient quantities to counteract the bad 

 influence of dark rooms, moisture, and poor air; yet, of all the bactericides 

 known there is none that compares in effectiveness with sunshine. Much 

 suffering would be saved if persons could only be brought to a realization 

 of this fact. Airing and ventilating bedrooms, kitchens, cellars, and 

 stables aids much in keeping them wholesome. 



Drying 



About thirty per cent moisture is required for the growth of bacteria. 

 This fact is the principle utilized in the preservation of many of our foods. 

 In order to preserve seeds we dry them, and they do not begin to sprout 

 until they are moistened when needed for planting. Flour is practically 

 free from decomposition because it is dry, and a cracker keeps indefinitely 

 for the same reason. In some regions, tons of fish are prepared for market 

 by drying. Fruits, such as berries, raisins, apricots, currants, prunes, and 

 apples, are preserved in this way. Dried beef has long been a familiar 

 example of the application of this principle. It must be remembered 



