The rate a t which different sugars cross the placenta varies from sugar to sugar. The aldoses glucose and d( +)xylose are exampIes of rapidly crossing sugars, whereas the ketohexoses sorbose and fructose pass the placenta slowly. It has been assumed that the permeability of the placenta to d( + )xylose is of a similar nature as that to glucose; the permeability to sorbose is comparable with that to fructose (KARVONEN et al., in press). D( + )xylose and sorbose may thus be used as tracer analogues to glucose and fructose, respectively, due to the inability of the organism to metabolize the foreign sugars.The purpose of the present study was to compare the placental permeability of sugars under normal conditions t,o those existing when the mother is kept under hypoxia or hyperoxia, by making it breathe different oxygen-nitrogen mixtures. Material and Nethods.Guinea pigs were used as experimental animals. They were anaesthetized with Nembutal intraperitoneally. The foetuses were delivered through caesarean section into a 0.9 yo NaCl bath kept at 38" C, where they remained connected with a functioning placenta. The foetuses were weighed after the experiment; their exact age was not known.

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Summary. Effect of thermal stress (Finnish Sauna‐bath) and muscular exercise (on treadmill) on the rise in body temperature, on the sweating rate, and electrolyte and lactate content of sweat is studied. In one half of the experiments, hypoglycaemia was induced by intravenous injections of insulin. There are no significant differences in the rate of sweating and in the composition of sweat during insulin hypoglycaemia and during euglycaemia. In the lactiite content of sweat there is some tendency to increased values with decreased blood sugar concentrations. The rise in body temperature under insulin hppoglycaemia is significantly lower than in experiments without insulin injection. The reason for this observation is briefly discussed.