The need of some improvement in our methods of determining the gastric functions is evident when we consider the limitations of the present methods. For instance, if after the administration of an ordinary test breakfast we aspirate an excessively large amount of contents, it is impossible to say whether the excess is due to abnormal secretion of gastric juice, to impaired motility, or to both. If, however, we should introduce with the test meal a certain amount of some substance which was not affected by gastric ferments, or absorbed by the stomach, something which would mix thoroughly with the gastric juice, then by estimating the amount left at the end of a given period we could determine how much of the test meal had passed on into the intestine; i. e., the gastric motility, and how much of the aspirated contents consisted of test meal, how much