Sir – It is disappointing to read Claudia Tarry's letter (D&S letters, July 19) containing, as it does, the usual mixture of half-truths, distortions and black propaganda designed to suggest to your readers that animal experimentation is somehow akin to wicked children pulling the wings off butterflies.

I can offer no better rebuttal than that provided by Hannah Devlin in The Times of July 17th., when she says: " testing on animals has been involved in almost every medical treatment that is available today - [for example] antibiotics, insulin, cancer drugs, heart surgery and organ transplantation. Treatments are also in the pipeline for rare genetic diseases such as Duchenne muscular dystrophy and motor neurone disease thanks to trials using genetically modified mice".

Claudia Tarry also tries to revive the old canard that animal experiments are worthless because of important differences between animals and humans, but a few minutes research will disprove this.

Anyone who compares a veterinary drug formulary with a human one will see that 90 per cent of the drugs which they contain are the same; how could this be true unless animal and human bodily mechanisms were also broadly the same?

ROGER A FISKEN Burneston, Bedale.