INTRODUCTORY NOTE
The experimental work in this paper was done during October, November and December, 1909, and January, 1910. A report of the work was made before the St. Louis Medical Science Club in February, 1910. The work was repeated during the year 1911 and read before the St. Louis Society of Internal Medicine in May, 1911. About this time our attention was called to the work of Hata, which was unknown to us. This work is practically identical with our method except in some points of technic. Hata's paper was published in November, 1909. After reading this paper we decided not to publish our results. As Hata's work has received practically no attention, it seemed important to us that this work should be known. It is a valuable method for the quantitative determination of pepsin. We submit this paper as a confirmation of Hata's work. We think our