What is the relationship between cows and immunization?

From ancient times, there were attempts to prevent
contagious diseases, such as smallpox, with a mortality rate of
30%.

At the end of the eighteenth century, when he was
the apprentice of a country surgeon in Berkeley, Edward Jenner (1749 - 1823), has noted
the followings. The farm milkmaids, who have had the vaccine disease (cow pox, which
causes a milder form of the disease), then they was no longer sick of human
smallpox.
Jenner called the substance, used for transmission of cow pox,
vaccine, after the latin name of this disease (Latin name is vaccine, derived from Latin
name Vacca, which means cow).

Jenner called the
process, used to protect against smallpox, as vaccination process. Medical world
was reluctant at first, to this new process. They subsequently have ended by accepting
the method of vaccination. This method has expanded rapidly in Europe, although the
cause of the disease was unknown.

In 1857, Louis Pasteur
has demonstrated that infectious diseases are caused by microorganisms, which can be
grown and studied. He formulated the theory of pathogens in 1864.

In 1876, Robert Koch has discovered Bacillus anthracis
and, in 1881, Mycobacterium tuberculosis.

In 1880, Pasteur
has proved that, by injecting weakened microorganisms into the body, it can provide
protection against infectious diseases.