On the number of nodes of Ranvier in different stages of the growth of nerve fibres in the frog

SINCE the early researches of Ranvier and Kdlliker it has been well known that the distance between two of the structures known as 'nodes of Ranvier' in a nerve fibre is subject to considerable variations; further, that this internodal length (or internode as it may be called) is less in young than in old animals, and less in narrow than in wide fibres'. During the increase in lerngth of a inerve fibre there migbt be either (1) an increase in the number of internodes, or (2) an increase in the length of internodes, their total number remaining the same, or (3) a combination of both processes. It is the object of the present research to determine which of these changes actually occurs. My experiments so far have been made upon frogs. The method used is briefly as follows:-the total length of the sciatic nerve is mieasured, the average length of a single initernode is found, and thus the total number of internodes in a single fibre running the whole length of the sciatic may be ascertained in frogs of different sizes. If this number remains approximately constant in large and small frogs, it follows that with the increase in length of the nerve there is an approximately corresponding increase in the length in each internode. The application of this apparently simple method becomes however less simple in actual practice, and each step in the process introduces possible errors. What is the best criterion of the "size" of the different animals? In this series two measurements have been made-(1) the total fresh weight and (2) the total length from the tip of the nose to the end of