20 BACTERIOLOGY 



produce disease under certain conditions, the name 

 pathogenic bacteria is practically synonymous with 

 parasitic bacteria. 



N on- pathogenic bacteria are those which do not pro- 

 duce disease, and are, for the most part, saprophytic. 



Stains. Different germs behave differently toward 

 various pigments when brought in contact with them. 

 Advantage is taken of this fact in diagnosis, germs being 

 differentiated in many cases by their staining or failing 

 to stain with a certain stain. It also assists in recog- 

 nizing their presence in tissue sections. 



Temperature. Some bacteria grow and multiply at a 

 temperature as low as o C. (32 F.), while others 

 flourish at 70 C. (158 F.). Pathogenic bacteria thrive 

 better at about the temperature of the human body. 

 While cold stops the growth and multiplication of these 

 forms, it is destructive to but few of them. Higher 

 temperatures they do not endure so well, and a tempera- 

 ture of 60 C. (140 F.) for a prolonged period is destruc- 

 tive to the majority of forms. A much higher tempera- 

 ture for a short time may be harmless, and freezing and 

 thawing several times is destructive to very many forms. 

 Spores, as mentioned before, withstand greater degrees 

 of either heat or cold than the bacteria themselves. 



Moisture is absolutely necessary to the growth and 

 multiplication of bacteria. Drying is fatal to a few 

 forms, as the cholera spirillum, but merely prevents the 

 growth of the majority of species. 



