1. The processes of repair in the kidneys of guinea pigs after sublethal doses of certain arsenical compounds indicate that all arsenicals do not produce a purely vascular type of renal injury.
2. While some arsenicals produce a predominantly vascular injury and others produce a predominantly tubular injury, both these tissue elements are undoubtedly always affected, although in varying proportion. In addition, the interstitial connective tissue is probably always affected. The diffuse proliferation of this tissue may be relatively conspicuous in the processes of repair after arsenicals that cause but slight vascular injury.
3. All red kidneys do not necessarily show identical pictures during the processes of repair; the same is true of pale kidneys.
4. The mode of action of an arsenical compound as a renal toxic agent is bound up with the chemical constitution of the compound.