54 INFECTIOUS AND PARASITIC DISEASES. 



tion of the infectious agents may be so wide-spread as to 

 make actual contact between the usual disinfectants 

 and the infectious agents (an essential condition for 

 satisfactory disinfection) absolutely impossible. Un- 

 der the several circumstances enumerated, it is self- 

 evident how valuable is the knowledge of the conditions 

 most favorable to the growth of bacteria, since by 

 removing favoring conditions and substituting harmful 

 ones, we can make use of most excellent means for 

 exterminating them. In the discussion which follows, 

 only the conditions favorable to the growth of patho- 

 genic bacteria are treated. 



There are five factors principally concerned in the 

 growth of bacteria, any alterations of which may be 

 regarded as distinctly unfavorable; these relate to food, 

 moisture, temperature, light, and relation to oxygen. 



Pathogenic bacteria require organic (albu- 

 FooD. minous) material upon which to feed. 



It makes little difference what the source, 

 whether vegetable or animal, solid or fluid, fresh or 

 putrid, they are adapted to all kinds. The blood and 

 tissues-juices of the animal body form an especially 

 good medium. Besides being albuminous, the material 

 must have an alkaline reaction. Nearly all bacteria 

 grow best in a slightly alkaline medium, and high 

 alkalinity, or moderate acidity, either stays their growth 

 or destroys them. Hence the strong acids and alkalies 

 are true disinfectants. 



