and are found aligned along myelinating axons. In older cultures, in which 

 myelinization is less active, this enzymatic activity subsides. 



Neurons of dorsal-root ganglia are low in suCcinic dehydrogenase and 

 DPN diaphorase activity during the first week, but a great increase occurs 

 duringthe second week, and maximal reactions occur at the time of myelin 

 formation. In capsule and Schwann cells, perinuclear DPN diaphorase is 

 found in the early stage of devëlopment, succinic dehydrogenase and TPN 

 diaphorase becoming active only in the second week. A remaricàble in- 

 crease of activity in Schwann cells occurs just before myelin appearance; 

 the enzyraesare then found throu^out the elongated cytoplasmic envelope. 

 Activity subsides as myelination becomes completed. 



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