Principle of Immunisation
Like many other major discoveries and inventions, the principle of immunisation was also discovered through one of those "happy accidents".
Louise Pasteur was working on fowl cholera when his experiments were interrupted by a vacation on which he fell ill. When he returned to work, he found that, to his disappointment, nearly all his cultures had become sterile. He tried to revive them by sub-inoculation into broth and injection into fowls. His sub-cultures failed to grow and the birds were not affected.
Getting resigned to his failure, Pasteur was about to discard everything and start afresh when he had the inspiration of re-inoculating the same fowls with a fresh culture. To his surprise, the birds which had been injected with the sterile culture earlier, survived while the fresh birds succumbed to inoculation. This chance occurrence resulted in the principle of immunisation.
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