The action of variable amounts of tridymite, and of tridymite combined with coal, on the lungs of rats.

Abstract

It was first shown by Gardner (1938a and b) in animal experiments that tridymite appeared to be more fibrogenie than quartz when tested by intra venous injection in rabbits. In fact, all his animals injected with tridymite died by 11 weeks. King, Mohanty, Harrison, and Nagelschmidt (1953a) used intratracheal injections into the lungs of rats, and compared well graded pure samples of quartz and tridymite, with the result that tridymite produced grade 5 fibrosis after nine weeks as against 38 weeks for quartz. The tridymite sample used had been in contact with hydrofluoric acid during purification, and as it had been found in other experiments (King and others, 1953b) that quartz etched with hydrofluoric acid also was more fibrogenic than normal quartz, there remained a suspicion that a trace of hydrofluoric acid had been the cause of the extra activity of tridymite. A new series of experiments was therefore set up with another sample of tridymite which had never been in contact with hydrofluoric acid. This sample was used at three different levels of dosage (12-5, 25, and 50 mg. per rat), and electro-dialyzed tridymite which was free from any adsorbed ions was also used at the 25 mg. per rat level. The fibrogenic activity of quartz and other materials has in the past been expressed solely on the basis of the degree of maturity of the lesions and the following five grades of fibrosis were used : grade 1, loose reticulin fibres with no collagen formation ; grade 2, compact reticulin fibres with or without collagen formation ; grade 3, slightly cellular but mostly collagenous ; grade 4, wholly collagenous and completely acellular ; and grade 5, acellular, collagenous and confluent. It has been felt for some time that this was not entirely satisfactory for quantitative assessments because the amount as well as the degree of fibrosis should be measured. Various attempts at an area assessment from microscope slides, and to use radiography of air-inflated rats' lungs, did not prove successful, but a quantitative estimation of collagen (Stacy and King, 1954) from dried lung material proved to be possible, and this technique was used to measure the fibrogenic activity of tridymite. Similar data for quartz were available, and this allowed equal dosages of quartz and tridymite to be compared. It had been found previously (Ray, King, and Harrison, 1951) that 2 mg. of quartz did not produce any fibrosis in the lungs of rats, but did produce fibrosis of the lymph nodes, into which all of it appeared to have been moved, when given alone. A mixture of 2 mg. of quartz and 98 mg. of coal did, however, produce fibrosis up to grade 2 after five months in the lungs of rats. Similar experiments with smaller amounts of dust were also made with tridymite and two samples of coal.