66 ESSENTIALS OF BACTERIOLOGY. 



(Fig. 41.) The culture can be forced through or allowed to filter 

 slowly. 



The germless liquor is then treated with various agents, 

 alcohol and acetic acid being that used for the toxalbumen of 

 diphtheria, and arwhite amorphous powder is at length obtained. 

 These agents have different effects in different doses, and are 

 used also to establish an immunity. 



Anti-toxins are obtained by filtering through a Chamberland 

 filter the serum of animals made artificially immune. 



They cause immunity when injected into other animals, or euro 

 the already developed disease. The anti-toxins of pneumonia, 

 tetanus, diphtheria, and erysipelas of swine have been istihitul. 



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. 

 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. 



