In the Tarentino, black sheep are not injured by eating the Hypericum crispum--a species of St.John's-wort--which kills white sheep.

White terriers suffer most from distemper; white chickens from the gapes.

White-haired horses or cattle are subject to cutaneous diseases from which the dark coloured are free; while, both in Thuringia and the West Indies, it has been noticed that white or pale coloured cattle are much more troubled by flies than are those which are brown or black.

The same law even extends to insects, for it is found that silkworms which produce white cocoons resist the fungus disease much better than do those which produce yellow cocoons.[59] Among plants, we have in North America green and yellow-fruited plums not affected by a disease that attacked the purple-fruited varieties.

Yellow-fleshed peaches suffer more from disease than white-fleshed kinds.