John Jacob Abel to successfully isolate the neutral base of epinephrine by adding ammonium to highly concentrated extract, a method Abel himself tried but failed due to the use of low concentration of extract. After Takamine's success, Abel himself remarked, with great candor, "The efforts of years on my part in this once mysterious field of suprarenal, medullary biochemistry, marred by blunders as they were, eventuated, then, in the isolation of the hormone not in the form of the free base but in that of its monobenzoyl derivative." Together with L.G. Rowntree and B.B. Turner, Abel devised what they called a "vividiffusion" apparatus,
John Jacob Abel some preliminary experiments on the subject, Abel decided to take on the research, and replied to his friend, "Will attack insulin. Writing. J. J. Abel." Abel invested the next few years on purifying insulin. While he was trying various means to purify insulin, he had the idea to measure sulfur content of his extracts and found that the higher the sulfur content, the greater the activity. The discovery not only significantly precipitated progress on extracting active fractions but also offered the very first concrete information on the structure of insulin—sulfur is an integral part of insulin molecules. Continuing with his