THE REGENERATIVE CYCLE OF MOTONEURONS, WITH SPECIAL REFERENCE TO PHOSPHATASE ACTIVITY.

1. The regenerative cycle of motoneurons after axon amputation is described, and an attempt made to correlate morphological and chemical events in cell bodies with the growth requirements of regenerating axons. 2. The "normal" pattern of Nissl material in the cell is considered to be the resultant of a steady state in cytoplasmic nucleoprotein. Chromatol is then interpreted as a shift of the balance of nucleoprotein turnover in fa of degradation. The rapid early depletion of Nissl substance in chromatolysis is ascribed to the increased growth requirements created by the active early sprouting of the regenerating axon. Acid phosphatase activity begins to increase above normal levels during this period in the region of nucleopro degradation. 3. The recovery period of chromatolysis due to axon section coincide in time with the phase of gradual lengthening of the regenerating axon, and is thought to represent a gradual restoration of the balance of nucleoprotein degradation and synthesis. During this period acid phosphatase activity is at its height in the region of transformation of Nissl substance, later declines to normal levels when the original pattern of Nissl bodie is restored. 4. The transformation of cytoplasmic nucleoprotein which occurs in chromatolysis after axon section, with the probable liberation (46), and depletion (44), of nucleotides, associated with acid phosphatase activity, suggests the hypothesis that liberated nucleotides or nucleotide compounds may pass down the axon in which they take part in enzymatic activity associated with growth and organization of the newly formed axon. This type of activity would not be incompatible with the ideas previously expressed (30, 81) of a continual function of Nissl substance in maintaining the integrity of the large volume of cytoplasm represented by the axon, as well perhaps as the associated myelin sheath.