Tests of functional activity appeal to the clinician who is confronted with an uncertain diagnosis or who is anxious to evaluate the results of treatment. He desires objective data to correct or amplify his clinical impressions. Admirable examples of successful methods of measuring the function of organs are the Graham test as applied to the gallbladder and the urea or the creatinine ratio measurement of renal activity. These tests are not intended to disclose the cause of disease but to indicate whether function is normal or subnormal at the time the observations are made. Other functional tests are less satisfactory but in some cases are of distinct value in studying hepatic or cardiac conditions.
The study of gastric acidity is relatively old but until recently occupied an anomalous position among functional tests. It was not used to measure how much gastric function had been impaired by disease but to indicate