BACTERIA 



307 



melting snow and ice scatter them far and wide over the 

 land and sea and destroy many of them. 



422. Disease-Producing Bacteria. Many kinds of bacteria 

 are harmless to our bodies, while others under certain 



conditions are the cause of sick- 

 ness and death. Thus, diphtheria, 

 typhoid fever, consumption, and 

 probably other diseases may be 

 produced through the agency of 

 certain kinds of bacteria. 



Surface soils abound in many 

 species of microorganisms which 

 ma y retam their vitality and viru- 

 lence for a long time. Thus, one 

 experimenter kept some typhoid 

 fever bacteria alive in polluted 

 soil for four hundred and fifty-six 



days. The disease called "lockjaw " is known to be due to 



germs occurring in the soil of certain localities (Fig. 199). 

 It is a mistake to think that a cut 



of the thumb or great toe is more 



likely to be followed by lockjaw than 



is a cut elsewhere. The germs of 



lockjaw may enter any open wound. 



423. Bacteria in Food. Food, 

 both good and bad, abounds in bac- 



teria. Fortunately not all bacteria FlG . I93> scrapings from the 



are harmful and many that are Teeth, containing Several 



harmful are destroyed in cooking. 



The typhoid fever germ has been 



traced to ice, ice cream, and raw oysters that were fattened 



in salt water polluted with sewage. Bacteria have a special 



FIG. 192. A Group of Soil 



Different Kinds of Bacteria. 

 Highly ma s nified - 



