In order to obtain data concerning the function of the cells which clear the blood of large particles, the velocity of removal from this fluid of colloidal thorium after intravenous injection was determined under normal conditions for dogs subsequently subjected to procedures designed to alter the activity of these cells.
There have been several previous studies of reticuloendothelial activity, determining the rate of removal of injected large molecular masses in the form of bacteria,1 colloidal metals (silver,2 manganese3 and saccharated ferric oxide4), quartz,5 carbon,2a egg yolk,6 egg albumin,7 bilirubin8 and various dyes (congo red,9 brilliant vital red,10 trypan blue,11 bromsulphalein12 and a series of acid and basic dyes13). Difficulties follow the use of all these substances which do not attend the use of thorium. All the dye studies have been complicated by excretion from the organism during the test period, so that the rate of removal