PRINCIPLES OF VETERINARY SURGERY 159 



may carry the bacteria from the pharyngeal cavities into 

 the stomach, or out of the body by way of the mouth and 

 nose. The food stuffs also may carry the bacteria into the 

 stomach. There are numerous saprophytic or non-patho- 

 genic bacteria all along the alimentary tract which may 

 antagonize and destroy the pathogenic bacteria. 



The conjunctiva rids itself of bacteria chiefly by remov- 

 ing them mechanically and washing them down through the 

 lachrymal duct into the nasal cavity. The mucous mem- 

 brane of the nasal cavity throws off the bacteria by its 

 secretions, aided by the ciliary action of the epithelium. 

 The stomach destroys bacteria through the action of the 

 hydrochloric acid. Few bacteria can live in an acid medium. 

 The vagina is normally free from pathogenic bacteria, 

 owing to the fact that there are constantly present in the 

 vagina saprophytic bacteria which have an acid secretion — 

 the bacillus Doederlein, for example. 



One of the most important means of defense which the 

 body possesses is the blood. Normal blood-serum, even 

 when free from leucocytes, is toxic for bacteria; and further- 

 more, it not only destroys these vegetable cells, but ani- 

 mal cells also. Whether the power exists primarily in the 

 serum or is one conferred on it by the leucocytes, leads to 

 the discussion of the two great theories of immunity. 



METCHNIKOFF THEORY : — Phagocytosis. — Eli 

 Metchnikoff, the distinguished biologist and bacteriologist, 

 who is now one of the heads of the Pasteur Institute in 

 Paris, and successor to Pasteur, first gave his theory of 

 phagocytosis to the world in an address given at Odessa, 

 before the congress of naturalists and medical men in 1883; 

 and since that time by many ingenious experiments and 

 much painstaking work has been constantly adding new 

 proof to his primary hypothesis, until now many bacter- 

 iologists believe that his theory satisfactorily explains im- 



