In 1796, Jenner demonstrated that inoculation with cowpox could protect against smallpox. Later, Pasteur developed similar vaccinations, which mobilized an immune response.
Intact skin is an important barrier.
The normal microbial inhabitants of the gut and vagina keep the growth of pathogens in check. Ciliated, mucous membranes in the respiratory tract sweep out bacteria and particles. Exocrine glands secrete lysozymes, which degrade the bacterial cell wall. Urine, with its low pH and flushing action, keeps pathogens from the urinary tract. Nonspecific and Specific Responses Phagocytic cells and antimicrobial substances are in place even before pathogens invade.