8 DUST AND ITS DANGERS. 



dead and worn-out organic material and setting 

 it free in suitable condition for the building up 

 of new forms of life. A few species of bacteria, 

 however, are capable of causing some of the 

 most wide-spread and most dreaded of human 

 diseases. 



The writer has in another book ' described 

 in simple and untechnical manner the various 

 forms of bacteria and their relationship to man, 

 and to this he must refer the reader for fur- 

 ther details as to their nature and life history. 



The moist surfaces of decaying vegetables 

 and plants and the bodies of animals, all solid 

 excreta of the bodies of men and animals, 

 human sputum, stagnant water, the surface of 

 the soil in inhabited regions, etc., afford fertile 

 fields of growth for myriads of micro-organisms 

 of one kind or another. 



But we should always remember that bacte- 

 ria do not become detached from the surfaces 

 or materials on which they grow or are lodged 

 while these are in the moist condition. Even 

 the air sweeping in strong currents through 

 sewers whose watery contents and moist walls 



1 " The Story of the Bacteria." 



