Pasteur saved the silk industry of France, and perhaps of the whole world, by the application of this law of artificial selection.

The disease of silkworms, known as Pebrine, was spreading with ruinous rapidity in France.

Pasteur demonstrated that the germ of the disease could be detected in the blood of affected moths by the aid of the microscope.

He proved that the eggs of diseased moths produced unhealthy worms, and he advised that the eggs of each moth be kept apart, until the moth was examined for germs.

If these were found, the eggs were to be burned.
Thus the eggs of unhealthy moths were never hatched, and artificial selection of healthy stock stamped out a disease, and saved a great industry.
Each individual plant in the struggle for life has only itself to maintain.