4 APPLIED IMMUNOLOGY 



a process designed to resist infection, if that be its 

 cause, and proves successful for mechanical and im- 

 munological reasons, if the reactive forces of the in- 

 dividual be capable. The invading bacteria develop a 

 condition of positive chemotaxis and leucocytes 

 swarm to the battle-field. Already the bacteria have 

 stimulated the tissue cells to the production of specific 

 substances or antibodies and many bacteria are killed 

 by lysis (see Chapter XI) ; the remainder, by virtue 

 of sensitization with their specific antibodies (opsonins 

 of Chapter XX), are ingested and destroyed by the 

 phagocytes (see Chapter XVII). While the mortal 

 conflict between bacteria and bacteriolysins and phag- 

 ocytes is being waged, inflammatory exudate and 

 proliferation of fi:xed tissue cells occur and raise bar- 

 riers to the further extension of the morbid process. 

 Coincidently, the antibodies are formed in excess and 

 impregnate the blood-serum, establishing the phenom- 

 enon of immunity. 



There is little evidence pointing to the presence of 

 natural antitoxic substances in animals, although they 

 have been claimed to occur to a limited extent in horses 

 and more abundantly in children and adults. Natu- 

 ral antibacterial substances are more extensively de- 

 monstrable in the tissue fluids and blood-serum. 

 Buchner has given the name " alexins " to these nor- 

 mal bacteriolytic substances. They appear to be 



