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Rawaa ("Animal tests 'upsetting but important'", March 19) is a young scientist who believes her experiments on rats are relevant to humans.

As she progresses, however, she will discover that an artificially induced disease in an animal cannot accurately represent the human condition.

Results can differ even between different strains of the same species, and scientists are unable to unravel the thousands of chemical and biological reactions a drug triggers in the human body. The action of medicines also differs from person to person. Age, sex, race, diet and lifestyle play a part - something the alternative professions have always known and practised.

Marlene Thompson
Hucknall, Nottinghamshire