PRINCIPLES OF VETERINARY SURGERY 157 



Whatever the type of immunity occurring, it is either 

 antitoxic or antibacterial. The serum of an animal im- 

 mune to tetanus is antitoxic ; for it is the extracellular toxin 

 of the tetanus bacillus which does the harm, and not the 

 mere body of the bacillus itself, which never comes in con- 

 tact with the tissue it destroys. Its toxin, however, goes 

 into solution and is carried from the wound to the nervous 

 system, — the bacteria remaining at their place of en- 

 trance, — and there destroys the tissue. Hence it is the 

 toxin which must be neutralized by a serum immune to 

 tetanus, and the immunity is in a peculiar sense antitoxic. 

 On the other hand, immunity to the cholera vibrio is anti- 

 bacterial. The toxin of the cholera vibrio is intracellular, 

 and is never diffused in a soluble form, so that the bacteria 

 themselves must come in contact with the tissues they are 

 to destroy. Experiments seem to show that the serum of 

 an animal immune to cholera, is able to kill the bacteria, 

 but apparently is not able to neutralize their intracellular 

 toxins which are liberated only after the bacteria are dis- 

 integrated. Such immunity is antibacterial. It is obvious, 

 therefore, that immunity, whether natural or acquired, may 

 be in one case antitoxic and in another antibacterial. 



Antibacterial immunity does not always imply a bac- 

 tericidal serum. For example, the dog and rat both are 

 immune to anthrax, yet the serum of the dog has no bacteri- 

 cidal effect on the anthrax bacillus, while that of the rat 

 is strongly bactericidal. This would indicate that the 

 serum is not the only factor governing an immunity. In 

 the same way immunity to toxins is not in all cases anti- 

 toxic in the sense that the serum contains demonstrable 

 antitoxin which will neutralize and render innocuous its 

 corresponding toxin. 



