The investigators present further observations in support of Bell''s hypothesis concerning chorionic epithelium and malignant tissue. Using Warburg''s (Berlin) technique, the authors estimated the respiration, aerobic and anaerobic glycolysis, and then calculated the U values for full term and about [image] term human placentae. In the former human serum and in the latter amniotic fluid were used as media. Positive Uvalues were obtained with placental tissue containing chorionic epithelium demonstrating the ability of this tissue to glycolyse aerobically, a power not exhibited by placental tissue containing no chorionic epithelium. By means of the glass electrode, using Kerridge''s technique, the p h of placenta, fetal tissues and malignant tumors was estimated and found to be on the acid side of neutrality, differing from adult tissues. Amniotic fluid is definitely acid, contrary to all text-book teaching. The umbilical vein contains much more lactic acid than the maternal artery; glucose values are the reverse of this. The acidity of the blood of the fetus is greater than that of the mother. In discussing the results, the writers point out that there are 2 main issues for decision: "The extent to which the fetal metabolism is responsible for the lactic acid in the blood of the umbilical vessels and the part, if any, played by the metabolism of the chorionic epithelium in this respect," and conclude that the lactic acid content of umbilical vessels is mainly of fetal origin, but that its source is difficult to determine as there is no muscular activity and no evidence that full-term somatic tissues can glycolyse when fully oxygenated. The suggestion is made that it is probably due to glycolysis by the trophoblast, especially in the earlier stages of pregnancy. The chorionic epithelium behaves functionally like a malignant neoplasm.