fewer suffer from the former.The degree of coronary atheroma discovered in persons killed accidentally has been studied in many parts of the world, and the condition has been found to be equally widely distributed in the United States and United Kingdom.Yet, in contrast, the mortality from ischaemic heart disease is markedly different in com- parable populations, the U.S.A.F.: R.A.F.ratio approximating to 10: 1.2 The opinion expressed by Kannel3 that it is the presence of an effective collateral circulation which determines the clinical picture offers a reasonable explanation of the anomaly.Carboxyhaemoglobin is easily determined and is therefore a convenient marker of the products of com-bustion.It is possible that, because of this, carbon monoxide is being artificially promoted as a cause of disease.Workers in Los Angeles4 have attempted to relate atmospheric CO levels to an increased fatality rate from myocardial infarction; in fact, any relationship must be attributed to atmospheric pollution as a whole.In the same way, postmortem studies designed to show atherogenic properties of cigarette smoke5 fail to take into account the life style of heavy smokers.The case for an association between smoking and ischaemic heart disease seems proved beyond doubt.But rather than to attribute an atherogenic property to cigarettes in general and carbon monoxide in particular (Dr.Wald and his colleagues do not claimn this to be necessarily so), it might be more valid, and in keeping with the "collateral" theory, to suggest that the carboxyhaemoglobin results reported by them were more significantly reflecting the levels of nicotine, which is known to have a marked pharmacological effect on the cardiovascular system.-I am, etc.,
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Kew et al. (1973) studied this question.