56 INFECTIOUS AND PARASITIC DISEASES. 



According as bacteria grow in the presence or absence 

 of oxygen they are called aerobes or anaerobes resiptctiYely. 

 Most of the aerobic bacteria grow as well without free 

 oxygen as with it, for which reason they are spoken of as 

 facultative anaerobes; but the contrary is not true; there 

 are few facultative aerobes. 



All bacteria grow best when protected 



Light. from light. This statement holds good 

 whether the light be natural or artificial. 



These five factors are the chief ones favorable to the 

 growth of bacteria, and to the retention of their native 

 characteristics and qualities. Variations in favoring 

 factors, if not sufficient to destroy them, always tend to 

 modify their functions (prevent growth, etc.), alter their 

 qualities (diminish virulence), and, to a certain extent, 

 produce variations in form. Broadly speaking, varia- 

 tions acting in this way are antiseptics as opposed to 

 disinfectants, which latter are the means used to destroy 

 bacteria. Modifications in favoring factors are all 

 the time in nature acting to reduce the rapidity of 

 multiplication of bacteria, or to prevent it entirely; 

 or by destroying their virulence to curtail their power 

 to do harm. Most excellent use has been made of our 

 knowledge of the growth of bacteria both in clinical 

 and preventive medicine. In the treatment of wounds 

 suspected of containing the tetanus bacillus, it is the 

 practice to leave the wound exposed to the air, because 

 we know that the tetanus bacillus will not grow in the 



