40 PRINCIPLES OF VETERINARY SURGERY 



the injury to the tissue is brought about by their poisonous 

 products — toxins. These toxic substances are definite chemi- 

 cal bodies which differ greatly in the different species of bac- 

 teria. They consist of toxalbumins. It is not always nec- 

 essary for the bacteria to be present in order to produce their 

 lesions or diseases. They can be grown upon artificial cul- 

 ture media and their toxins can be separated out by a pro- 

 cess of filtration and injected into an animal, and the same 

 symptomalogy and changes in the tissue will occur as if the 

 bacteria were allowed to multiply and produce their toxins 

 in the tissue themselves. 



Many bacteria have a selective action, i. e., they have an 

 affinity for certain tissues of the body. For example, the 

 toxin of tetanus bacilli have an afifinity for brain tissue and 

 no matter where they gain entrance into the body, their 

 toxins must reach the nerve cells before they can do any 

 harm. Bacillus coli communis has an affinity for the gastro- 

 intestinal tract; anthrax, for the blood; the tubercle bacillus, 

 for the lymph-glands ; the virus of hydrophobia, for ixervous 

 tissue ; while other bacteria may act principally on the 

 parenchymatous organs — the liver, spleen and kidney. In the 

 human, the gonococcus has a great affinity for the urethra, 

 the diphtheria bacillus for the throat; while on the other 

 hand, such bacteria as streptococcus and staphylococcus will 

 produce their lesions in any part of the body. Staphylococci 

 will make an abscess in the withers as readily as in the kid- 

 ney. The streptococci may produce a skin-lesion, or an in- 

 flammation of the uterus, or a general infection of the blood, 

 — septicaemia. There are also certain non-pathogenic bac- 

 teria, whose products — ptomaines — may set up indirectly a 

 slight inflammatory process. 



There are other factors which influence a bacterial in- 

 flammation besides the bacteria themselves. These we call 

 predisposing causes. First is susceptibiHty ; an animal's tis- 



