Animal sacrifice goes back a long way. The basic idea is that you put all of your negative energy into a virgin or a goat and then kill her.

The evil goes off along with the victim and everybody else can breathe a sigh of relief. The story of Jesus dying on the cross "so that we could be forgiven for our sins" seems to be related to this idea. Surprisingly, product testing works in much the same way.

When a new product is launched, its toxicity and irritancy must be measured using two standard tests: LD-50 and the Draize test. In the LD-50 test, groups of animals are given different amounts of the substance: the object is to see how much of it is needed to kill half of the test animals in a group.

In the Draize test, the substance is put into the eyes of a group of rabbits. The animals are immobilized, and after a couple of weeks their eyes are examined. Depending on the substance, they might just be swollen, or have completely disintegrated. During this time, the animals are in constant pain.

For example, the test substance thiourea gives a value of 4 mg/kg in Hopkin's rats and from 1,340 to 1,830 mg/kg in Norwegian rats. It is probably safe to assume that Hopkin's rats are more closely related to Norwegian rats than either type is to humans. Results also differ depending on the time of year, the food that the animals have been eating, and the number of animals in the cage.

Nor are the figures much use in clinical practice. Dr Christopher Smith, a board-certified emergency medicine physician in the US, says that he knows of no instance in which an emergency physician has used Draize test data to aid in the management of an eye injury. Nor has he ever used LD-50 data to manage accidental poisoning. As he and many other toxicologists point out, it is much more useful to know symptoms, treatment and the results of clinical trials in humans.

Results from LD-50 tests are used to label new products. Despite the fact that values may vary a thousand-fold between different substances, there are only three to six categories, depending on the scheme. In any case, very different LD-50 values are used in different countries. While it is certainly useful to know which substances are toxic, LD-50 values give a spurious air of precision to what is inevitably a very crude judgement.

Nor is the Draize test any more valuable. The FDA lost a major court case following an incident in which a woman splashed shampoo in her eye because they were unable to show that results obtained in rabbits were relevant to humans. Yet this was the only purpose which the test ever had.

So why do the tests continue? A central argument made by those people who support them is that it is better for a rat to die than for a human. This is debatable. In any case, the two are not even connected. If the data are not actually used, the only link is a psychological one.

Zbinden, a toxicology consultant for the World Health Organisation, agrees. He describes the LD-50 test as "a ritual mass execution of animals".

Perhaps one can think of a new toxic substance as having both positive energy and negative energy: it can be used for good purposes (such as cleaning a dirty lavatory) but it has a negative side as well (it kills you if you drink it). Instead of asking people not to drink it, the negative energy is put into a group of sacrificial animals. The animals are killed, and we are saved. Hallelujah!