200 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



with the mucosa being preferentially permeable to the unionized form of weak 

 electrolytes (91). These considerations make it more reasonable to assume that 

 carbonic and lactic acids have to cross micelles of a distinctive pH and perme- 

 ability character rather than to assume that their apparent transport is due to 

 selectively specific mechanisms. Calculation suggests that buffer diflfusion into 

 the gastric tubule of the spontaneously secreting isolated frog mucosa would 

 not materially change the pH within the tubule for most of its length. The 

 tubule would then have a distinctively low pH, its ostia would not discriminate 

 between CO2 and HCOs^, and its cellular border would be expected to be 

 preferentially permeable to unionized CO2. This provides a plausible if trivial 

 answer to the apparent active transport of carbonic acid. Thus, experimental 

 evidence, sought to substantiate forced anion exchange, is in point of fact 

 non-decisive. 



REFERENCES 



1. Bradford, N. M. and R. E. Davies. The site of hydrochloric acid production in the 

 stomach as determined by indicators. Biochem. J. 46: 414-420, 1950. 



2. Browne, J. S. L. and A. M. Vineberg. The interdependence of gastric secretion and 

 the CO2 content of the blood. J. Physiol. 75: 345-365, 1932. 



3. BucHER, G. R., C. E. Anderson and C. S. Robinson. Chemical changes produced in 

 isotonic solutions of sodium sulfate and sodium chloride by the small intestine of the 

 dog. Am. J. Physiol. 163: 1-13, 1950. 



4. Conway, E. J. Exchanges of K, Na and H ions between the cell and its environment. 

 Irish J. M. Sc. Oct-Nov. 1947: 1-44, 1947. 



5. Conway, E. J. The biochemistry of gastric acid secretion. Springfield: Thomas, 1953. 

 185 pp. 



6. Conway, E. J. A redox pump for the biological performance of osmotic work and its 

 relation to the kinetics of free diffusion across membranes. In: Bourne, G. H. and J. F. 

 Danielli. Int. Rev. Cytology II: 419-445, New York: Acad. Press, 1953. 



7. Crane, E. E. and R. E. D.avies. Electrical potential difference and resistance of isolated 

 frog gastric mucosa and other secretory membranes. Tr. Farad. Soc. 46: 598-610, 1950. 



8. Crane, E. E., R. E. Davies, and N. M. Longmuir. Relations between hydrochloric 

 acid secretion and electrical phenomena in frog gastric mucosa. Biochem. J. 43: 321- 

 336, 1948. 



9. Crane, E. E., R. E. Davies, and N. M. Longmuir. The effect of electric current in 

 HCl secretion by isolated frog gastric mucosa. Biochem. J. 43: 336-342, 1948. 



ID. D'Agostino, a., et al. Alterations in the ionic composition of isotonic saline solution 

 instilled into the colon. J. Clin. Investigation 32: 444-448, 1953. 



11. Dalton, a. J. Electron micrography of epithelial cells of the gastrointestinal tract and 

 pancreas. Am. J. Anat. 89: 109-133, 1951. 



12. Davenport, H. W. The inhibition of carbonic anhydrase and of gastric acid secretion 

 by thiocyanate. Am. J. Physiol. 129: 505-514, 1940. 



13. Davenport, H. W. The secretion of iodide by the gastric mucosa. Gastroenterology 

 i: 1055-1061, 1943. 



14. Davenport, H. W. Substrate and oxygen consumption during gastric secretion. Feder- 

 ation Proc. 11: 715-721, 1952. 



15. Davenport, H. W. and V. J. Chavre. Conditions affecting acid secretion by mouse 

 stomachs in vitro. Gastroenterology 15: 467-480, 1950. 



