Progressive degenerative changes in ageing temporal arteries are described. These changes are usually severe in elderly patients, hence their presence in diagnostic biopsies provides no evidence of temporal arteritis past or present.In two patients in the series of random necropsies examined there were changes in the temporal arteries identical with those seen in patients known to have suffered from temporal arteritis in the past; in both these cases there was, in addition a giant cell aortitis.The distinction between healed arteritis and degenerative changes due to age in a single biopsy specimen may be difficult. Furthermore, it is possible that steroid treatment may arrest the progress of the disease so that gross intimal thickening and vascularization of the artery wall do not occur.Giant cell arteritis is not a rare disease. Two examples were discovered in 39 random necropsies on patients over 60 years of age.

MEDBRsOH reliable to take a continuous series of instantaneous samples, say, every minute for an hour, and give the maximum, minimum, and mean values ? In addition to the questions which Dr. Handley Howell raises, data as to wind speed and weather conditions for each test would be helpful. It would also be useful to carry out the tests at various times of day, including times of peak travel. Nevertheless, the results at first sight seemed reassuring, but unfortunately Commins et al. omitted to mention that Saltzman's6 method (which they used for estimating oxides of nitrogen) is actually a method of estimating nitrogen dioxide only-it is not sensitive to nitric oxide. According to Faith7 the major component by far of oxides of nitrogen from internal combustion engines is nitric oxide. This gas is important, partly because of its direct toxic effects and partly because it is steadily converted to nitrogen dioxide in the atmosphere. This conversion may well occur more readily in tissues such as the lungs in the presence of oxidizing enzymes. Perhaps Commins et al. could give some figures for total oxides of nitrogen. I note that Commins et al. emphasize "the limited significance of the preliminary garage results." Would that much of the popular and the motor press had emphasized this instead of giving the report misleading publicity. Assuming that the London Transport Executive realizes this limited significance, surely it is its duty to admit that the diesel engine has not yet been proved harmless to health.-I am, etc., London, E.4. F. G. TOMLINS.

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