DISTRIBUTION OF CONTAGIOUS DISEASES 211 



multiplying are the most prominent facts to be borne in 

 mind when contending with contagious diseases. We 

 must not, therefore, think that anything is safe from 

 contamination with bacteria because it looks clean. The 

 eye may not see the contamination even when it is present. 

 Clear, sparkling water may sometimes contain deadly bac- 

 teria, while dirty water may be perfectly safe to drink. 

 Nor must we think any substance safe because it has only 

 an extremely small quantity of infectious material upon it, 

 for bacteria can grow so rapidly that a half dozen may 

 become millions in a few hours if they have a chance 

 to feed and grow. 



