The penetration depth of different color solutions into the dentine substance of teeth still in the jaw, freshly extracted and older teeth from collections has been compared with that of chlorine and ozone gas. Non-organic impedients within the dk as well as undamaged cement are hereby not penetrated; organic residues are influenced depending upon the chemical characteristics of the gases. How much self-blocking caused by albumen metabolism of fresh Tomes' fibers took place, could not safely be determined. Fat-containing substrates are penetrated slowly in vitro by chlorine, albumen significantly quicker. The reaction of cytozon gas is similar, however, the reactions deviate timewise.