What corpuscles characterized silkworm pébrine in Pasteur's work?

The corpuscles that characterized silkworm pébrine in Pasteur’s work were Cornalia corpuscles.

Pébrine, meaning “pepper disease,” devastated silkworm farms in southern France and produced dark spots on infected larvae. In 1865, chemist Jean-Baptiste Dumas asked Pasteur to investigate the crisis. Pasteur examined the disease microscopically and described the conspicuous corpuscles associated with it.

Pasteur initially treated the corpuscles as symptoms, but by 1870 he recognized their causal importance and showed that pébrine could be inherited through infected eggs. His practical solution was to inspect crushed pupae or moth tissue under a microscope and reject breeding stock containing corpuscles.

The name is an easy source of confusion: these are not human blood-cell structures such as Barr bodies, pressure-sensing Pacinian corpuscles, or the inclusion bodies associated with rabies known as Negri bodies. Modern biology identifies the main causal organism as the microsporidian Nosema bombycis.