400 journal of Comparative Neurology and Psychology. 



age. Such a shrinkage of the cell body will naturally, as suggested 

 above, stretch this part, the medullated portion being probably 

 much less plastic. It is hardly probable, however, that all of 

 the diminution in thickness of this portion of the axone is artifici- 

 ally produced, inasmuch as it has been demonstrated by so many 

 methods (isolation, Golgi, Ehrlich, Cajal). 



With a single exception (see below) no sign of any collateral 

 branch for the naked part of the axone has been noted, but this 

 cannot be regarded as negative evidence of much weight, for the 

 stain is obviously only capable of demonstrating comparatively 

 coarse structures. In the exception noted there is a small process 

 given off from the distal part of the cone which could not be 

 follow^ed far, owing either to its terminating or, more probably, 

 having been decolorized. It is not a termination of some fiber 

 upon the surface. In other imperfectly decolorized sections, how- 

 ever, strands can be seen crossing the pericellular space, similar to 

 those described by NissL and others. In certain cases these bear 

 some resemblance to the pericellular terminations of Auerbach. 



Beyond the narrow portion the axone expands and at the same 

 place becomes medullated (axis cylinder). This expansion may 

 be rather gradual (Figs. 3, 4 and 5) or quite abrupt (Figs, i and 2). 

 At the same time there is usually an apparent deepening of the 

 stain. This is probably due partly to the increase in size and 

 partly to the presence of the stained myelin sheath above and 

 below the axis cylinder. Considering the well known tendency of 

 the axis cylinders to shrink, they would appear to be fairly well 

 fixed in these preparations. 



The increase in size of the axone always coincides with the 

 appearance of the myelin sheath. Furthermore, there seems to be 

 often a correlation between its mode of expansion and the appear- 

 ance of the sheath; when the former expands abruptly, the sheath 

 appears to attain its full size also abruptly. The sheath is often 

 distorted considerably by the fixation, etc., and exhibits alternating 

 contractions and vesicular expansions. This is shown especially 

 in Figs. I, 3 and 5. In other cases (Figs. 2 and 4), the fixation 

 is better. Owing probably to local contraction, there are places 

 where it is difficult to demonstrate the presence of the sheath, as is 

 indicated in the figures. A close study of the relations at the 

 point of origin of the sheath with the sheath better fixed is still 

 desirable. 



