The kindest cut?

Laboratory experiments appear to demonstrate how the foreskin appear to be especially vulnerable to attack by the virus, which has killed millions in sub-Saharan Africa alone.

While some argue that encouraging circumcision in populations which have no historic tradition of the procedure amounts to mutilation, many scientists are convinced that many lives could be saved this way.

The latest experiments, carried out at the Children's Memorial Hospital in Chicago, US, took samples of the tissues of the foreskin kept alive in culture and deliberately exposed them to the virus.

They found that cells in the tissues called Langerhans cells actually reached out to grab the virus, draw it into the tissue, and even transport it to the lymph glands, from where it can begin its assault on the immune system.

The key is the amount of a substance called keratin on the surface of the skin.

On most skin, this forms a solid layer which is impervious to viruses and bacteria - but on the mucosal surfaces such as is found on parts of the foreskin, there is less keratin.

The scientists in Chicago found that when areas of the foreskin which had the keratin layer were exposed to the virus, infection did not take place.

'Dramatic findings'

Dr Bruce Patterson, who led the study, said: "The most dramatic findings are the ease with which the foreskin is infected and the extent to which it is infected.

"If this is a primary tissue involved in transmission of HIV and we are capable of removing it, we should remove it."

There is a growing weight of statistical evidence that uncircumcised men seem to be far more at risk of contracting the Aids virus than circumcised men.

Early studies were contradictory, with some even suggesting that circumcised men were more at risk.

However, more sophisticated reanalysis of these results has reversed the conclusions.

The BBC Horizon documentary will be screened on BBC2 on Thursday November 16 at 2100 GMT.