The experimenter then watches for signs of abnormal reactions, such as over-activity, tremors, convulsions, hair standing on end, spasms of muscles, diarrhoea, bloody discharge from the rectum, dribbling of saliva, watering of the eyes, incoordinated staggering movements, slow, rapid or irregular breathing, barking, squealing, screaming, whining or moaning, bulging of the eyeballs, writhing etc.

Sometimes the experimenter administers the substance, departs the laboratory for his evening's pursuits (evening meal, television, and as they are almost always "animal lovers" walking the 'family dog') to return to the laboratory the following morning to count the dead: there can not be an around the clock surveillance of the poisoned animal prisoners.

Half the animals die within 14 days. The remainder teeter on the brink of death and on recovery are used in the next test series. There are no survivors - and no anaesthetics or pain relief is ever used in the Lethal Dose 50 Test.

The following extract from Veterinary Record, November 21 1968, pages 653-655 is all too explicit:

Virus Research Department
Tasman Vaccine Laboratory
Upper Hutt
New Zealand

"Cats were obtained from suppliers located principally in the Hamilton and Auckland areas of the North Island of New Zealand. All ages were represented in the 222 animals involved in this study.

On arrival, the cats were identified, bled by cardiac puncture and immediately forcefed with 1.5 ml of a 20 per cent suspension of virulent panleucopenia virus-infected kitten intestine. These animals were observed several times daily and post-mortem examinations were made on those found dead or destroyed when in extremis . Wherever possible cardiac blood smears were examined to confirm the specific cause of death, but otherwise reliance was placed on the gross physical appearance of the mesenteric lymph-nodes and ileum.

Following dosing with virulent virus the majority of deaths fell mainly within the subsequent six to 11 days. Cats dying after the 13th day post infection were excluded from the series. Throughout the six weeks' duration of the experiment no intercurrent respiratory disease was noticed among the test population."

Why the LD50?

The chemical industry in a Press Release of 9 December 1977 stated that:

"the LD50 is the most misrepresented and misused of all indices of toxic activity of chemicals".

The Chemical Industries Association represents 90% of the chemical industry's output.

Bill McMillan, Director of the Chemical Industries Association in U.K. is reported to have said they wanted to reduce the number of experiments...

"but where you have a substance which is being exported and governments and transport agencies require a number to fill in on their little bits of paper - we're saddled with the LD50".

In the U.K. Department of Health and Social Security stated (Hansard, November 24 1981) that:

"LD50 results are required by drug regulatory authorities in countries to which we export, contributing to a net favourable balance of trade in pharmaceuticals of over five hundred million pounds sterling".