How Did Pasteur Discover The Method Of Making Vaccine?

Vaccination is the method of cultivating weakend germs.Pasteur discovered this method by accident.He was working of fowl-cholera in 1879.He went away on holiday.When he retured he found all his cultivations of the germs dead or dying.He inoculated various birds with those dead or dying germs and found that the birds showed signs of illness but recovered.Then he injected fresh germs of chicken-cholera to them.Now those birds had developed resistance against the disease though other which were not previously inoculated with weakend germs,died.Thus he arrived at the method of cultivating germs so that they were weakend.This was the method of preparing vaccine.