Mental Illness-Shepherd et al. MEDBCAL JOURNAL 1363 and for the detection of causal associations among these complex conditions. At the same time the study underlines the need to extend and refine available techniques of measurement. Even with carefully defined criteria of illness the wide variation between practitioners' prevalence rates points to two potent groups of factors. The first of these relates to the ecological differences between practices and can be offset by paying regard to the size and representativeness of the sample of participating doctors. The second relates to the doctor, his attitudes, and his interactions with his patients ; for psychiatric illness, as we have shown, they constitute a major source of variation. SummaryThis paper reports on a general practice survey of psychiatric morbidity carried out in the Greater London area. The sickness experience of nearly 15,000 patients on the lists of 80 practitioners was studied over a period of one year. It was shown that minor psychiatric disorders, classified according to a predetermined schema, were diagnosed in 14% of the population at risk. Neurotic illness was most prevalent among middle-aged females and proved to be an important cause of chronic illness. The reasons for interpractice variation in recorded morbidity are discussed.We are grateful to the following general practitioners, whose cooperation made this study possible. (1957, 1961) found a high incidence in a post-mortem series of patients who had had a cerebrovascular accident, but they did not study any control subjects; they suggested that extracranial arterial disease was a common cause of cerebral infarction through its direct effect on cerebral blood flow. Schwartz and Mitchell (1961) showed that atherosclerosis of these arteries, as with atherosclerosis elsewhere, correlated well with age, that it was common even in patients without cerebrovascular accidents, and that a correlation between cerebral infarction and extracranial atherosclerosis could be due largely to the fact that both were correlated with age. The occlusive lesions described by these authors varied from small plaques scarcely narrowing the arterial lumen to complete occlusion of one or more of the extracranial arteries. The incomplete lesions were classified, according to the percentage reduction of the normal lumen, into mild or moderate (less than 50% reduction) or severe (more than 50% reduction); no evidence is available to assess the possible effects of such stenosis on cerebral blood flow.Alteration of calibre may be of importance either directly, by its effect on cerebrovascular resistance, or indirectly, producing turbulent conditions of flow which might predispose to local platelet aggregation. In this paper we are concerned with the effect of narrowing of carotid arteries on their hydraulic resistance only, and report experiments designed to determine the approximate dimensions and hydraulic resistance of the minimum narrowing which has a detectable effect on blood flow through the artery. We...

We investigated the effects of Antarctic residence (AR) on serum thyroid hormone and cardiovascular responses to a 60-min standard cold air (0 degree C) test (SCAT). Serum total thyroxine (TT4) and serum total triiodothyronine (TT3), free T4 (FT4) and T3 (FT3), thyrotropin (TSH), and percent free fraction of T4 (%FT4) and T3 (%FT3) were measured in normal men (n = 15) before and after each of three SCATs. The SCAT was first carried out in California and then repeated after 24 and 44 wk AR. Mean arterial pressure (MAP) and sublingual oral temperature (Tor) were measured before and during each SCAT. The SCAT did not alter thyroid hormones before or after AR. The %FT4 decreased from 0.0334 +/- 0.0017 to 0.0295 +/- 0.0007% (P less than 0.002) with 44 wk AR but without a significant change in TT4 or FT4 for the same period. The %FT3 also decreased from 0.2812 +/- 0.0128 to 0.2458 +/- 0.0067% (P less than 0.005) after 44 wk AR. FT3 decreased (P less than 0.003) but TT3 and TSH were unchanged with 44 wk AR. The decrease in %FT4 and %FT3 may be theoretically accounted for by a 10% increase in either the capacity or the affinity of the serum binding proteins. The SCAT in California increased MAP and did not change Tor. After 44 wk AR, the SCAT no longer increased MAP but did lower Tor. The shift in the Tor and MAP response to the SCAT is consistent with the associated occurrence of cold adaptation during AR. We describe for the first time a decrease in the free fraction of both serum T3 and T4 present with extended polar residence and independent of a SCAT, further characterizing the recently reported "polar T3 syndrome."