BACTERIOLOGY. 165 



Saprophytic and Parasitic Bacteria. The bacteria 

 that grow on dead organic matter is called sapro- 

 phytic, the variety that grow on living organic matter 

 is called parasitic. 



The variability of bacteria is of much importance, 

 since the line of demarcation is not yet definitely de- 

 termined. 



The death of bacteria is usually determined by the 

 fact that in a medium in which they were growing 

 luxuriantly, on inoculating a new supply of the same 

 medium they fail to grow. 



Those agents which kill the greatest number of bac- 

 teria in the shortest time are carbolic acid and bi- 

 chloride of mercury (the first in a solution of I to 

 1,000; the second in a solution of I to 20.) 



These are called germicides. Those agents that so 

 alter the medium that bacteria will not grow on it are 

 called antiseptics. 



The best germicides are heat, acids and the heavy 

 metals in solution. Muir and Ritchie. 



CULTIVATION OF BACTERIA. 



In order to study bacteria, it is necessary to have 

 them growing apart from other bacteria. In nature 

 this is not so since they are mixed up in general in the 

 medium; it is only in the blood and tissues that we 



