Vhiution of Total Circzhting Hemoglobin and Reticzclocyte CozGnt of Man with Season and Following Hemowhagel

I T IS NOW WELL ESTABLISHED that change in environmental temperature alters blood volume (I-S). D uring periods of a few days of exposure to heat, blood volume increases at first by simple dilution and later by increase in the amount of circulating plasma protein. As a result, hemoglobin con-centration declines by 5 to IO per cent below values obtained at comfortable temperatures. There may also be an increase in quantity of circulating hemoglobin. However, this increase must be considerably less than re-ported originally by Barcroft (3), since recent investigators have found total circulating hemoglobin to change only slightly (4) or to remain constant in such experiments (I, 2). Opposite effects follow exposure to cold. The imluence of season on blood volume has been studied less thor-oughly. As a result of seasonal changes in environmental temperature, one might expect that blood volume and hemoglobin concentration would change as in the experiments cited above. The fact that a significant seasonal variation in normal hemoglobin concentrations has not been found clinicall