Harat, Sheaths of the Peripheral Nerves. 151 
can best be seen by examining the cross-section of the nerve 
fibers. 
Fig. 1 shows the cross-section of the peripheral nerve of 
the cat, treated by the method mentioned above. The neuro- 
keratin stains an intense pink, while the rest of the structure 
remains for the most part unstained ; the axis cylinder presents, 
however, a faint blue tint. It may easily be seen that each 
fiber shows the double rings of the neurokeratin, one along the 
outer margin and the other along the inner margin of the me- 
dullary sheath. These rings, however, are not complete cir- 
cles, but appear as broken lines or are composed of dots. The 
size as well as number of the dots in each ring is variable. In 
some cases, instead of minute dots, a continuous long line is 
noticed, and in still other cases filaments more or less tangential 
to the inner ring are observed. The latter appearance is more 
common in the rings which immediately surround the axis 
cylinder. In some cases, these two rings are connected with 
each other by means of threads of neurokeratin which run per- 
pendicularly to the long axis of the fibers and in cross-sections 
give an appearance of radiations from the central ring; in other 
words, wheel-like structures are formed by means of connecting 
bands between the two rings. The manner of the distribution 
of the connecting band is so irregular that it is almost impossi - 
ble to give a general description of all the different appearances. 
I can merely state that the number of the connecting bands just 
mentioned is not constant, sometimes six or seven being ob- 
served and in some cases more than a dozen. Furthermore, 
the spaces formed by the connecting bands are also variable in 
size and shape. Some of the connecting bands are united with 
others by means of the delicate side-branches which they give 
off. In some instances, three rings are noticed (Fig. 1,4). The 
reason for this irregular distribution of the neurokeratin in the 
cross-section of the nerve fibers is easily understood if one ex- 
amines the longitudinal sections of the same fibers, and to these 
we now turn. 
The longitudinal view of the nerve fibers is shown in 
Figures 2, 3 and 4. The preparations were made from the peri- 
