Mouse skin painting

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This article is part of the Tobacco portal on Sourcewatch funded from 2006 - 2009 by the American Legacy Foundation.

Mouse skin painting was a standard 'bio-assay' test used to determine whether various chemicals or substances are likely to be cancerous. Generally a specially-bred hairless mouse is used in fairly large numbers, and the substance is painted onto a standard patch of skin on a regular basis with some of the mice only. Others from the same batch get no skin-painting.

This was the most cost-effective way to investigate chemicals (pesticides, herbicides) which may enter the food supply, and to check cigarette smoke, etc. for its propensity to produce cancers.

Of course it is always open to objections. Not all rodents react the same (rats are particularly resistant). Nor are all 'strains' of mice (they are specially bred for this type of research). The comparison is always made between those who have been painted, and those which have not -- and the protocol demands that each of these two groups are treated in exactly the same way (same food, cleaning routine, day-to-day handling ... down to being painted with water instead of the chemical under investigation. (not a requirement that is always followed)

• in smoking studies, the aim is to identify the "fractions" of the chemicals which produce the skin tumours. This is a reference to the different distillation products extracted from the complex chemical make-up of the "condensate" -- which is the condensed form of tobacco smoke. The preparation of these condensates must also be standardised, and also the extractions of the various fractions. These processes sometimes involve chemical solvents, which must themselves be proved not to be cancer-forming.

• The lifetime of a mouse is only a year to 18 months, so the solution being painted must, of necessity, be more concentrated that they would expect to find in the lungs of a smoker who may smoke for 20 years before getting cancerous changes in the tissues.

Hockett Dictum

The Hockett dictum was an catch-phrase created by Robert C Hockett, the Scientific Director of the Council for Tobacco Research in order to discount discoveries of cancerous substances in the smoke condensate. He opined that it was ""The use of the wrong materials, in the wrong form, in the wrong concentration, under he wrong circumstances, on the wrong animal." At a later stage he used a reduced form: " ... the wrong material, the wrong tissue, the wrong animal. Man is not a rodent."

Of course this claim discounted generations of laboratory studies of diseases of all kind.

Inhalation studies

In parallel to mouse skin-painting was the inhalation by animals of actual cigarette smoke. It transpired that rodents, who needed to survive in garbage dumps etc. had very effective nasal hairs which reduced the effect of smoke particulates (the microscopic solids that make smoke visible) and so they were ineffective for inhalation studies ... which is why the tobacco companies favoured them to produce null results.

Eventually Syrian Golden Hamsters and Beagle Dogs were found to be ideal experimental animals for inhalation experiments. The research of Oscar Auerback, Freddy Homburger, and Walter Dontenwill all used these larger animals.