IT IS IMPORTANT TO KNOW, if possible, the underlying reasons for performing gastro-enterostomy and gastric resection for peptic ulcer. Particularly in a teaching clinic, engaged in training young surgeons, we should know why we advocate the surgical metlhods which we teach and how they achieve their effects. I need not, before this audience, take the time to discuss the reasons commonly advanced to explain why these procedures are effective or why they fail. Tn more recent years, as yotu are aware, the etiologic relationship between excessive acid and ulcer has been emnphasized tlhrouglh the experimental and clilnical work of Dragstedt, W7\aingensteell, and mllany otlhers, wlhose imiiportant work deserves more consideration than can be givell it in so slhort a presentation. As a result of this work some authors believe that the emiipiric surgical approach to the problem of ulcer in man can be abanidonied and may now be approached scientifically on the basis that the acid secreted by the stomach is the important factor in the causation of ulcer. Surgical procedures, therefore, which abolish or diminish acid gastric secretion may be expected, on this basis, to cure ulcer and prevent recurrence.It has been observed by a number of authors that gastro-enterostomy fails to alter acid secretioni. It does not, therefore, to many, meet the requirements of a surgical operation designed to cure ulcer, even though there is abundant evidence in the literature that it relieves the symptoms and protects the individual against the complications of ulcer in a fairly high percentage of cases. It has also been observed that gastric resection, if of sufficient magnitude, does diminish or abolish acid secretion and, therefore, more nearly meets the requirements of an ideal operation for the cure of ulcer. Certain authors have gone farther in their approach to the problem and find that not only resection, but specific types or methods of resection assure achlorhydria more certainly than others. Thus, for example, Wangensteen has found that with a resection of three-fourths of the stomach, and according to the Hofmeister or Finsterer exclusion method (the latter with excision of antral mucosa), 63 per cent of his patients are achlorhydric, and fail to develop gastrojejunal ulcer.It will be observed that the recent emphasis has been laid upon actual reduction or diminution of acid secretion by the removal of secretory gastric mucosa. The factors of dilution and neutralization of acid through surgical procedures-another possible explanation for their success if acid is the