Heinemann:
He examined how the body recognises itself and is able to use its immune system to respond to foreign substances, such as viruses, without invading its own cells in the process. he concluded that the ability to recognise self-substances cannot be inherited, but is gradually acquired in the course of fetal development. Due to constant contact with cells in the body at an early age, the develping immunity-producing tissue learns to recognise and remember its own pattern. Burnet predicted that if tissue from another body were introduced to a feotus at the right time, it would learn not to reject this foreign tissue.
By 1960 Burnet had also developed the clonal selection theory. This important theory has helped us to better understand the immune system and how our bodies learn to distinguish between self and non-self.