The quantitative determination of the variation of gastric acidity during different phases of digestion by the so-called "fractional method of gastric analysis" is presumably based on the assumption that the gastric chyme, after a test meal, is a homogeneous mixture, and that a small portion (from 6 to 10 c.c.), aspirated at fifteen minute intervals, represents the acid concentration of the gastric contents as a whole at that period of digestion. If this above hypothesis is correct, and if it is based on a true physiologic principle, then we should expect the acid concentration of different portions of the remaining gastric chyme to be similar at these different intervals after a test meal. It is my purpose to show that this hypothesis is not based on true physiology, and that the acidity of one portion, as obtained by the fractional method, may differ widely from the acidity of different portions