Claude Bernard and the Nature of Gastric Acid

CLAUDE BERNARD AND THE NATURE OF GASTRIC ACID THOMASJ. SERNKA* In his thesis for the M.D. degree in 1843, Claude Bernard concluded incorrectly that gastric acid was lactic rather than hydrochloric acid. Not only was he mistaken in this issue, but he also contradicted prior research leading to the correct conclusion. In 1824, William Prout had published his finding that gastric acid was hydrochloric [I]; and in 1833 William Beaumont published analyses of gastricjuice containing hydrochloric acid [2, p. 79]. To find out how such a great intellect as Bernard's could have been misled on so basic a problem as the chemical nature of gastric acid, my colleagues in the languages and I have translated Bernard 's published article with Barreswil on this subject in the Comptes rendus de l'académie des sciences, "Concerning the Chemical Phenomena of Digestion" [3]. Logically, Bernard approached this problem by first distinguishing free acid: "Two opinions prevail today in science on the cause of the acidity of the gastricjuice: in one, it is submitted that this characteristic is due to the presence of calcium biphosphate; in the other, it is attributed to an acid existing in the gastric juice in a free state." Bernard disposed of the calcium biphosphate origin of gastric acidity with directness: "... we have observed that the gastric juice dissolves neutral calcium phosphate, and we are sure that this salt is completely insoluble in the biphosphate of the same base. We have concluded from these experiments that the gastric juice acquires its acidity not from calcium biphosphate, but by the presence of a free acid." Of the many free acids, only four were considered possible gastric acids at that time: "... some [authors] acknowledge acetic acid, a greater number acknowledge hydrochloric acid, some phosphoric acid and others, finally, lactic acid." It is perhaps significant that Bernard *Associate professor of physiology, Wright State University School of Medicine, Dayton, Ohio 45435. I am grateful to Glenn Whitted and Doreen Roth (Case Western Reserve University) for their indispensable assistance in translating Bernard's and Melsen's articles.© 1979 by The University of Chicago. 0031-5982/79/2204-0068$01.00 Perspectives in Biology and Medicine ¦ Summer 1979 \ 523 mentioned his own choice last. Also, it is apparent that hydrochloric acid had the greatest number of proponents. Bernard and Barreswil proceeded to verify the presence of these free acids in gastric juice. No other acids were tested. They emphasized, in preface, that "... all [experiments] were done with very pure gastric juice, taken from several very productive dogs." In spite of this, it has been alleged that the contamination of gastricjuice with wood (from his cannulas?) might have led Bernard to find so much lactic acid [4, p. 51]. Acetic acid was sought by distillation of gastricjuice, since acetic acid is volatile: "... the first products collected and tested with litmus paper did not exhibit the acid reaction. As a counterproof we distilled water very faintly acidified with vinegar; the liquid which passed first in the distillation had an obviously acid reaction. . . . According to these experiments , it seems to prove to us that gastric juice does not include free acetic acid. ..." Note Bernard's elegant use of the counterproof method [4, p. 70] in this series. Acetic acid was absent from gastric juice if and only if added acetic acid (vinegar) was detectable by the same method (distillation). Since hydrochloric acid also is volatile, the distillation experiments might have led other less careful investigators to similarly rule out this possible source of gastric acid. For Bernard to have reached such a conclusion, however, ... we would have fallen in error, as is going to be seen by the following experiment . In effect, if one acidifies water very slightly with hydrochloric acid, then distills it, it is noted that there passes at first in the distillation only pure water, whereas the acid is concentrated in the final products, given off only at the end of the operation. This unexpected fact made us determined to distill pure fresh gastric juice in a distillation extending up to the dry point. We then have this observation: at first and throughout almost the duration of the experiment, there passes in the...