Silkworm jaundice virus is stable only between pH 5 and about pH 9. The fact that polyhedral bodies retain virus activity after exposure to hydrogen ion concentrations as high as pH 2 is regarded as being due to the protection of virus occluded within the bodies. Further evidence on this point is furnished by experiments on the activity of the polyhedra when treated with antiformin-formalin and when treated with 1 per cent sodium dodecyl sulfate. Free jaundice virus is inactivated by 36 per cent urea, 36 per cent guanidine, or 1 per cent sodium dodecyl sulfate. A purified preparation, active at a concentration of 10–12 gm. per cc., consisting essentially of a nucleoprotein component having a sedimentation constant of 17 S, a particle diameter of 10 mµ, and a molecular weight of about 300,000, was obtained from the polyhedra-free blood of jaundiced silkworms. However, a component having a sedimentation constant of 16 S was demonstrated in the blood of normal worms. This component, the material from diseased blood, and polyhedral bodies, were found to contain serologically related material. Absorption of material from diseased blood with antiserum induced by a preparation from normal blood yielded a substance having a sedimentation constant of 17 S, which reacted strongly only with antiserum to material from diseased blood. This fact, and especially the fact that the inoculation of normal blood does not produce jaundice, demonstrates that a difference must exist between the purified material from diseased worms and that from normal ones. Chemical analyses of the purified virus material and of the polyhedral bodies also showed certain differences, although both probably represent nucleoproteins. Examination by means of the electron microscope showed further differences.