A study of the transport and permeability properties of the guinea-pig amniotic membrane.

1. The simultaneous measurement of the two-way sodium flux across the in vitro amniotic epithelium did not reveal a preferential active movement of sodium in either direction. The amnion is thus unlikely to be the site of formation of amniotic fluid. 2. The permeability of the amniotic epithelium to some non-electrolytes has been measured with isotopes and was found to be generally low in relation to the thinness of the tissue. The permeability to non-electroytes would appear to be depebility to sodium and to non-electrolytes was found to vary with gestational age. The amnion from animals of 61-70 days' gestation was markedly more permanent than those at 50-60 days (term 70 days).