It is foreign to our subject to discuss here methods for the detection of so-called free and combined hydrochloric acid in the stomach-contents, or the special significance of such findings in health and disease. I cannot refrain, however, in connection with what has been said above concerning the proteolytic action of pepsin in the presence of combined acid, from saying a word concerning the usual deductions drawn from the absence of free acid in the stomach-contents. As Langermann[112] has recently expressed it, we have methods for discriminating between free and combined acid; we can, moreover, determine the amount of free acid, but is it not equally important to be able to say something definite concerning the amount of combined acid in the stomach-contents? Even in the absence of free hydrochloric acid there may be a sufficient amount of HCl secreted to answer all the purposes of digestion, and yet at no time may there be any free acid present to be detected by the various color-tests ordinarily made use of. I am aware that in ordinary examinations of the stomach-contents after a test meal the results are essentially comparative, and possibly all that are necessary for clinical purposes. What I wish to emphasize, however, is that in order to pass conclusively upon tsufficiency or insufficiency of the gastric secretion, it is wise to know not only the total acidity of the stomach contents and whether there is free acid or not, but to know more about the amount of combined acid present. Thus, there is a natural tendency to divide the fluids withdrawn from the stomach into three groups, viz., those which contain free acid in moderate amount, those which contain free acid in excess, and those in which free acid is entirely absent; but in the latter group, there may be very marked differences in the amount of acid combined with the proteid and other material present. It appears to me that one of the questions to be answered is whether there is sufficient combined HCl present to meet all the requirements for digestion. If there is, that gastric juice may be just as normal as the one containing free mineral acid, and yet, according to our present tendencies, we should be inclined to call the juice containing no free acid abnormal, although there may be sufficient combined acid present to meet all the requirements for digestion. Hence, in examination of the stomach-contents, it is well to consider the use of those methods which tend to throw light upon the amount of combined acid present, for in my opinion it is only by a determination of the total amount of combined acid that we can arrive at a true estimate of the extent of the HCl deficiency. Obviously, in simple clinical examinations of the stomach-contents after a test meal, where proteid matter is not present in large amount, free acid may reasonably be expected to appear after a definite period; but in any event, it is well to remember that free