1 8 BACTERIA 



aquatic forms of bacteria can live and grow in distilled water. The 

 addition of the various sugars is of advantage in the cultivation of 

 many bacteria, and glycerine for the growth of some members of 

 the Mycobacteriacece. Blood serum or whole blood is required by 

 some pathogenic organisms. The food stuffs must be in a form 

 that can diffuse through the cell wall. ^X 



^ The temperature of the medium in which various bacteria grow 

 is most important. Bacterial growth is possible between o C. and 

 70 C., some varieties thrive at the one extreme, and otrfers at the 

 other. < 



Psychrophilic bacterfa^ are those that grow at 15 C., with a 

 maximum of 30 C. and a minimum of o C. Water bacteria 

 of the polar seas belong to this group. 



Mesophilic grow best at 37 C. the temperature of the body 

 and thrive from 10 C. (minimum) to 45 C. (maximum). All 

 pathogenic bacteria belong to this group. 



Thermophilic (min. temp. 40 C., max. 60-70 C.) are most 

 prolific at 50-55 C. To this class belong bacteria of the soil. 

 All of this class are spore bearing. 



Darkness favors bacterial growth. 



^Association of different kinds of bacteria is of some importance 

 in their growth and welfare. When thus associated, they sometimes 

 benefit each other. Such combination is called symbiosis. jC 

 v Certain anaerobic bacteria grow i*T the presence of oxygen if 

 other particular varieties of aerobic bacteria are present./ 

 \ Attenuated tetanus bacilli become virulent if cultivated with Bac- 

 terium vulgae. Again, complicated chemical changes, as the decom- 

 position of nitrites with the evolution of nitrogen cannot be accom- 

 plished by certain bacteria severally, but jointly, this is quickly 

 brought about. "f" 



^Pfeiffer has shown that certain chemical substances (foods, albu- 

 mins, etc.), attract bacteria (positive chemotaotis) , while other sub- 

 stances, as turpentine, repel them (negative chemo taxis') . 



Oxygen repels anaerobes and is particularly attractive to aerobes. 



