(60) Jenner made a little cut on a boy's arm, took a small portion of pus in a cowpox scab on a mild-affected milkmaid's hand and inoculated it into the boy's arm. The boy felt slightly uncomfortable at first, but he became well and could play with other children soon.

(61) Jenner's inoculation experiment was successful. However, the most important thing was to inoculate on the little boy to test his resistance of smallpox. Jenner hesitated over the experiment. If the experiment failed, the boy would probably die of smallpox.

(62) When he considered that the experiment was for the benefits of all the smallpox patients, Jenner decided it worthwhile to take the risk. He took some pus from the smallpox of a patient and inoculated it on the boy's arm. It was a really worrying and torturing moment.

(63) Week after week, the boy was still as fit as a fiddle. The trial of inoculating against smallpox proved successful, and Jenner's success opened up a new field of medicine: immunology.

(64) Jenner's success inspired many scientists. In 1891, Emil von Behring, a German physician, found antitoxins in the serum to fight against Corynebacterium diphtheriae, and this serum therapy is still very valuable in the field of immunology.

(65) Scientists have made vaccines against smallpox, typhoid fever, cholera and many other infectious diseases. However, some diseases, like tuberculosis, still refused to submit until Albert Calmette and Camille Guérin, two French scientists, made a new contribution in this respect.

(66) As early as in 1907, Calmette and Guérin wanted to make a vaccine against tuberculosis.However, tuberculosis was so stubborn and abhorrent that while using dead tuberculosis bacteria as vaccine could not produce resistance, using live bacteria as vaccine would make people fall ill.

(67) Calmette and Guérin didn't give in. They isolated highly toxic tuberculosis bacteria forartificial culture. After 230 generations of vaccination, it took nearly 13 years for them to produce a live vaccine against tuberculosis.

(68) In honor of the two scientists who worked hard to invent vaccines, people call this vaccine BCG, which still plays an important role in the prevention and treatment of tuberculosis.

(69) However, not all infectious diseases had a vaccine or antiserum. Humans needed a new weapon to fight bacteria. In this counterattack, Paul Ehrlich of Germany opened a new chapter in the battle against bacteria.