On internodal length.

A study has been made of changes in internodal lengths in rat tibial nerves and human sural nerves with age. Myelinated fibre counts on these nerves showed that maximum numbers were reached at an early stage of development. The slope of regression lines relating internodal length to fibre diameter was relatively flat at this stage, but became steeper with increasing age. Maximum internodal length in rat tibial nerve was closely related to growth of the limb bones. Whilst this study confirms that the largest fibres are subjected to hind limb growth for the greatest period, and therefore have the longest internodes, it does not support the generally accepted view that short internodes are the consequence of the later myelination of small fibres, and hence shorter period of extension due to growth.