[Effect of marking laboratory animals on the results of pertussis vaccine potency tests]

White mice used for protection tests with pertussis vaccines when marked with fuchsin before challenge showed reduced survival rates compared with their equally treated but unmarked cage mates. The fuchsin used had been dissolved in denaturated alcohol. On account of the small amounts of marking material applied, there was probably no direct toxic effect. Further methods of marking have then been studied in this delicate test system. Contrary to expectations the marking with picric acid solution showed no adverse effect at all. The shearing of an area of the fur, however, resulted in an even more detrimental effect than the use of fuchsin. The clipping of the top of one ear rested below the level of significance. Most probably the marked mice were neither affected adversely by the handling when marked nor by an actual chemical or mechanical impairment, but by the initiation of stress induced by the majority of their unmarked cage mates. At any rate, a possible influence of the marking of animals on the result of test procedures should be carefully considered.