64 ESSENTIALS OF BACTERIOLOGY. 



(Fig. 37.) The culture can be forced through or allowed to filter 

 slowly. 



The gerraless liquor is then treated with various agents, 

 alcohol and acetic acid being that used for the loxalbumen of 

 diphtheria, and a white amorphous powder is at length obtained. 

 These agents have different effects in different doses, and are 

 used also to establish an immunity. 



Toxic Bacteria. Those bacteria which produce toxic agents 

 outside of the body, and will not develop in the body, are 

 called toxic bacteria. They are pathogenic only in the sense 

 that their products, when accidentally introduced into the body, 

 cause mischief. 



Infectious Microbes. Those bacteria which can develop and 

 do develop in the animal body, and there generate products 

 injurious to the same, are called infectious bacteria, or pathogenic 

 bacteria. 



The Variations of Pathogenesis, The same animals under 

 different circumstances can be differently affected by the same 

 germ. 



The ordinary white mouse is not acted upon by the bacillus 

 of glanders. 



If, however, glycosuria be produced in the mouse in any way, 

 it speedily becomes attacked by the bacillus. 



Different animals are differently affected by the same germs. 

 As we said before, ordinarily the white mouse is not acted upon 

 by the bacillus of glanders, but the house mouse is at all times. 



The bacterium may first become active when mixed with 

 certain chemicals, it having been harmless before. 



Attenuation or Weakened Virulence. Bacteria can be les- 

 sened in action either temporarily or permanently, or made in- 

 active entirely without destroying them. There are the natural 

 decay and loss of strength ; and successive cultivation in artificial 

 media for a long time of the same germ also destroys its potency. 

 But artificial means can be used, such as the use of chemical 

 agents added to the nutrient soil, or by passing the germ through 

 animals who are in some sense immune, and are less affected than 

 the animals for whom it is strictly pathogenic. 



Thus the bacillus of swine-erysipelas, which is quite virulent 



