ONE FIGUKEEarlier experiments on soluble phosphates in frog nerve (Gerard and Wallen, '29) showed the presence of a fraction, 'labile phosphate,' closely resembling in behavior the phosphagen or creatine-phosphate of muscle. A similar arginine-phosphate fraction has been studied in invertebrate nerve (Tang, Tang and Gerard, '32 ; Engel and Gerard, '35). The more complete identification of the nerve substance could be achieved by actual isolation, a rather thankless task when but a few milligrams of nerve are available per frog; or, for practical demands, by demonstrating a bound creatine fraction paralleling in stochiometric fashion the labile phosphate. The second procedure offered further opportunity of rechecking, by following changes in creatine, many of the conclusions drawn from the phosphate study. This alternative was chosen, and, as the work progressed, it became clear that we were in fact dealing with creatine-phosphate as one of the creatine fractions. Many additional data have been obtained as to its behavior under various treatments of nerve; and parallel studies with muscle have yielded similar but often distinctive results. Incidentally, interesting information concerning another chromogenic fraction has accumulated, especially from analysis of brain.
METHODS
1.Tissue. Nerves were dissected, with the usual precautions, into iced mortars. Unless in experimental solutions, they remained in moist gas (to obviate diffusional losses) usually hung from platinum electrodes 'Aided by a grant from the Rockefeller Foundation t o The Uiiiversity of Chicago. Summary reports of part of this work have appeared in: Proc. Soe.