UNCLASSIFIED Building service compressed air was dried and the pressure and flow suitably controlled. This air was then introduced into the Roller separator. The powder sample was placed in a U-shaped glass tube and the powder was suspended in the air stream by agitation of the tube with a mechanical tapper. The particle-laden air stream then entered the separating chamber. This chamber is designed in such a waythat only those particles with a given maximum terminal velocity are carried over into the animal exposure chamber. This terminal velocity is determined by the linear velocity of the air through the settling chamber. Those par: ticles having lower terminal velocities are returned to the inlet tube, and a mechanical tapper minimizes the tendency of the small particles to cling to the wall of the separating chamber. The animal exposure chamber is mounted directly over the separating chamber outlet. The generator provided a stream of airborne dry particles at a constant size and concentration level (0.2lmc/l). The animal chamber is exhausted - through a venturi mixer through which outside room air is also drawn, and then through a CWSfilter to remove the radioactive particles. The laboratory vacuum system serves as the exhaust for the filtered air stream. The entire systemismounted inside enclosures whichare main- tained at a pressure slightly below room pressure during operation. The safety precautions described are necessary to reduce to a minimum pos- sible hazard to laboratory personnel. RESULTS AND DISCUSSIONS Analysis of the distribution of Sr85 in mice exposed to the dry particle Sr8 Cl2 aerosol for 3 hours revealed that at 0.5 hours after expo- sure the activity of the G.I. tract and its contents was over 80 percent of the total activity in the mice. The distribution of Sr85 in the animal Rt hey F. , rm 3 ki be Pi FY i ry po pe ps pe ye a tissues (expressed as a percentage of the initial activity of the G.I. tract and its contents), is shown in Fig. 3A. The activity in the G.I. tract was almost 100 times that found in the lungs at this time. The large amount of Sr in the G.I. tract presumably resulted from the rapid clearance of the aerosol from the tracheo--bronchial tree and the nasopharyngeal region of the animal, and its subsequent ingestion.