UNCLASSIFIED only indicative. The respiratory rate of the animals, which influences the metabolism and therefore the uptake of the radioactive material, was probably altered by the operation, but since it was not measured in the experiment, an evaluation of the effect of this factor on the internal deposition is not possible. The influence of a soluble carrier (sea water) on SrCl, generated as a liquid aerosol as compared with a biologically inert carrier adminis tered as a dry particle was also studied. The ratio of activity in the G.I. tract as compared to that in the lung was approximately 50:1 for the liquid aerosol as compared to 100:1 for the dry particle aerosol at 0.5 hour after exposure (Table 2). Thus, it appears that the higher solubility of the carrier, the manner of association of SrCl2 with the carrier, or _ the administration of the aerosol in liquid form enabled more material to be absorbed and transported to the circulation and ultimately to be deposited in the bone. About three times as much Sr appears in the skeleton during the 28-day experimental period after exposure to the liquid aerosol as was observed following inhalation of the dry particle aerosol (Table 2). The ionic solution of Sr85cl>, and the suspension of Sr85¢12 dry particles were also administered by gavage as well as by inhalation. The tissue distribution of Sr when administered by the two methods is shown in Table 3. Again it was found that the ionic solution of SrCl2 was absorbed and retained by the tissue to a greater extent than the dry par- ticle SrCl2. About twice as much Sr administered in ionic solution was found in the skeleton as after the exposure to the dry particle suspension. The liver content was not significantly different after 2 hours following administration. Finally, a study was made of the uptake and distribution of the very insoluble La absorbed on the surface of an insoluble dry clay particle. to determine the extent to which such a particle can penetrate to the internal tissues. The La!#%) 3 was administered both by inhalation and gavage. The ratio of activity in the G.I. tract and its contents to that of the lungs and respiratory tract was about 75 at 1 hour after inhalation exposure (Table 4). At this time the liver had about 0.1 percent of the Ff LF Ie lo | j= pw [eH rs £E rm &@ ha F ry & ki £€ b Z ri ER 4 I> ln Ic iz 1a Ic activity in the G.I. tract, and the skeleton, about 0.6 percent. The head retains 5.8 percent of the G.I. activity at this time, consisting almost entirely of activity from material trapped in the naso--pharyngeal region.