As a science, immunology initially developed in parallel with and virtually as a branch of microbiology its primary concern being with the mechanisms involved in the development of resistance by the body to infectious diseases. That clinical attacks of certain diseases could confer a specific immunity or protection against a future attack of the diseases has been known from antiquity. This knowledge was first specifically applied to prevention of diseases in the practice of variolation and later of vaccination in the prophylaxis of smallpox.