503percentage uptake criterion is to be used a more realistic figure for a significant difference would be 8 % rather than 15%/,, with the usual collimator employed. However The use of the relative uptake index avoids the application of the same arbitrary limits for a positive diagnosis to all patients. The reported incidence of venous thrombosis detected by 12"I-fibrinogen is of the order of 300/4 (Flanc et al., 1968; Negus et al., 1968; Hills el al., 1972). On the basis of the results reported here this seems to us to be a low estimate. We have shown that the sensitivity of the method is increased when account is taken of variations in count rates and anatomy, so that the relative uptake index may well provide a more accurate indicator of the presence of deep vein thrombosis than those in current use. Caution must be advised, however, in estimating the incidence of thrombosis from the data reported here, because the patients studied were selected specially to give a high number of positive results.The method of counting does not differ from that commonly used, and the mathematical analysis is simple and suitable for routine use. By using the program daily results can be obtained a few minutes after the data have been fed into the computer. The computer program will also draw attention to anatomical points at which a significant change has occurred; this form of data processing saves a great deal of time both in the calculation and in the interpretation of the results.

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Fourteen healthy male subjects with hemagglutination-inhibition antibody titers of 1:8 or less to homologous influenza A virus were studied. Six subjects received live, attenuated influenza virus by nasal drops and by aerosol. Although infection occurred in these six subjects, with the development of 4-fold or greater increases in hemagglutination-inhibition antibody titers, they remained asymptomatic. Eight subjects received placebo via the same route, and did not develop symptoms and showed no increase in antibody titer. Prior to administration of virus or placebo, histamine diphosphate aerosol increased airway resistance only slightly, and there was no difference between the virus and placebo groups. Two days after inoculation, bronchomotor responses in the placebo group were unchanged (p greater than 0.05), but in the virus-infected group, bronchomotor responses were significantly greater than in the preinfected state (p less than 0.01). Isoproterenol hydrochloride reversed and prevented the increase in airway resistance after histamine, suggesting that the bronchoconstriction was caused by smooth muscle contraction. Our findings indicate that transient, asymptomatic respiratory virus infection augments airway smooth muscle responses.

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