A Summary of Studies on the Effect of Ferric Chloride on Tuberculous Rabbits. ∗

Abstract

The object of this brief report is to describe further experiments on the effect of ferric chloride on the progress of tuberculosis in rabbits previously immunized with a strain of BCG (Bacillus Calmette-Guerin) and subsequently reinfected with a virulent bovine strain of tubercle bacilli (Ravenel). Previous studies have demonstrated that concomitantly with the accumulation of iron in tuberculous areas the course of the disease in rabbits is definitely retarded. This has been shown in 4 independent series of experiments. 1 , 2 , 3 , 4 , 5 The mechanism to account for this favorable effect has not as yet been elucidated. The accumulation of iron in tuberculous areas is as a rule demonstrable not by microscopic test but only in the gross when the tuberculous lung tissue is in contact with acidified K₄Fe(CN)₆. Experiments previously described 6 have shown that this is in large part due to considerable loss of the iron presumably during the “clearing” stage in the technique of microscopic preparation. Parallel to the deposition of iron in tuberculous areas an intracellular iron pigment is also found by microscopic examination to be deposited in the spleen, liver, and bone marrow. The pigment is indistinguishable from hemosiderin, but is not referable to hemoglobin degradation. It has therefore been termed cytosiderin. 6 , 7 , 8 The presence of this iron pigment in various organs in addition to the non-pigmented form of the metal, seen in the gross within pulmonary tubercles, renders it difficult at present to account adequately for the beneficial effect of FeCl₃ in tuberculous rabbits. Furthermore a few preliminary experiments employing other iron compounds, or injection routes other than the intravenous one, fail to yield results identical with those obtained by the writer when large numbers of rabbits are repeatedly treated with dilute ferric chloride solution intravascularly. 9 In addition to the present set of data, a summary of all previous studies is tabulated (Table II).