“…The presence of these knots has been taken as an index of placental maturity and it has been stated that in the normal term placenta approximately 30 per cent of villi show such knots (Benirschke, 1962;Merrill, 1963). The corollary to this statement is, of course, that figures in excess of this imply excessive placental ageing, and such changes have been described in toxaemia of pregnancy (Riviere, 1930;Sauromo, 1953;Burstein et al, 1957;Shanklin, 1959;Becker and Bleyl, 1961 ;Merrill, 1963), in postmaturity (Kubli and Budliger, 1963), and diabetes mellitus (Burstein et al, 1957). Little mention has been made in these studies as to the placental area from which the blocks for examination were taken and in several cases counts were simply made from random high power fields.…”