GENERAL SCIENCE 



the disinfecting gas can get into every part of them. All 

 cracks and openings of the room should be stopped gas 

 tight. About a pint of the 40 per cent solution serves for a 

 room of ordinary size, and the room should be kept tightly 

 closed for twenty-four hours. Where sulphur is left burning 

 in the closed room there is always more or less danger of 

 fire, and the disinfection from sulphur 

 alone is less satisfactory. 



It needs to be emphasized that most 

 kinds of bacteria are harmless to man, 

 and many kinds are of the greatest im- 

 portance to his well-being. On the 

 roots of such plants as peas, beans, 

 clover, and alfalfa, certain bacteria 

 thrive that have the power to abstract 

 nitrogen from the atmosphere and 

 convert it into compounds. These 

 nitrogen compounds later serve as 

 plant food, thus increasing the fertility 

 of the soil. Other bacteria give to 

 butter and cheese their appetizing 

 By the multiplication of certain bac- 

 teria in sewage it is rendered harmless. If it were not 

 for the action of bacteria concerned in the decay of organic 

 matter, the collection of refuse material in thickly settled 

 sections would constitute an ever growing problem. 

 Carbon taken from the carbon dioxide of the air, and nitrogen 

 from soluble material as plant food in the soil, would thus, 

 rapidly become accumulated in dead organic bodies, and 

 be unavailable for plant growth. 



SUMMARY 



With the use of the term infection is associated the idea of disease 

 transmitted by germs. These germs are microscopic one-celled plants 

 known as bacteria, or are one-celled animals known as protozoa. In 



FIG. 17. The homes 

 of "nitrogen - fi xi ng" 

 bacteria. (Conn.) 



tastes and odors. 



