The Electron Microscopy of
Sectioned Nerve

George Rozaa,l Councilman Morgaa,
Albert Srent-Gy5rgyi,1 and Ralph W, G. Wyckoff

Laboratory of Pbyrkai Biology,
Experimental Biology and Medicine Institute,
Nattonal Inrtttsstes of Health,
Bethesda, Maryland

Nerve is one of the most important tissues for study
under the eleectron microscope both because knowledge
of its macromolecular structure is needed for an under-
standing of the mechanism of impulse propagation and
because this knowledge is essential for any study of the
neurotropic virus diseasea. Until recently little prog-
rees in such a atucly has been possible on account of the
large size and fragility of moat nerve fibers.  They can,
however, now be examined to great advantage in thin
eection.

Fro. 1.  An electron mfcroqraph of a longitudinal section
through a single fiber of myellnated nerve.  The flbrous eon-
tents of the central axon are dearly seen, as are the denser
lamellse of the surrounding myelin.  The thin neurllemma
enveloping the whole is visible at the very top and bottom of
the photograph.  Magnification, 6,000 x.

ZSpecial feIiows, Experimental Blologg and Medicine, Na-
tional Institutes of Health. U. 8. Public Health Service.

FIQ. 2.  A nearly transverse section through part of a
nerve bundle.  One fiber showing the eame structures aa Fig.
1 iIlls most of the picture.  Small parts of two other llbere
m-e in the lower right corner and the top, left of center.  A
band of connectfve tissue and the embedded sectioned tip of
another flber separate the lower flber from the one in the
center.  ~a~i~cation, 5,000 x.

Very recently preliminary electron micrographs have
bean published of sectioned nerve (1) but these photo-
graphs were of fibers that were so seriously damaged
during preparation that their fine structures and the
relation of these structures to one another were not, evi-
dent. We have found that excellent sections can be
obtained pf nerve prepared and cut according to the
techniques outlined by Newman, Borysko and Swerdlow
(2).  What is seen in such sections under the high reso-
lution of the electron mkroscope depends in marked
degree on the kind of fixation and dehydration used, and
it will require much experimentation with many reagents
to establish beyond doubt all aspects of the maeromoleeu-
lar texture of native nerve.  Nevertheless, nerve can now
be sectioned without disturbing its various components
and consequently a detailed study can now be begun of
its structure and of the changes caused by various pre-
parative reagents.

Results of a first set of such experiments are being
published elsewhere (3) but the accompanying photo-
graphs illustrate the kind of electron micrographs of
sectioned nerve that can readily be prepared, These

42

ScxENall, Vol. 11"


show a ion~tudi~l (Fig. l} and nearly transverse (Fig.
2) section through the serztus ischio~io~s of the adult
rabbit fixed in 4%. formalin and dehydrated in one (laae
in ethyl alcohol and in the other ,with pyridine.  In the
longitudinal section one can see the filamentous fine struc-
ture of the central axon and the more "opaque " lamellar
texture of the nonlipid portion of the enveloping myelin
sheath.  The neuril~ma outside this and the absence of
an axilemma of similar structure between axon and
myelin are apparent.  The same structures are visible in
Fig. 2; which also gives an idea of the relation of a nerve
fiber to the connective tissue elements with which it ie
associated in a complete nerve bundle.  This photograph
likewise brings out the fact that in many parts of narve
fibers the texture of the lamellae of the myelin is less
coarse in the region immediately enveloping the axon.
Other photographs we.have made both at these and at
higher magnidcations show the fine details of the struc-
tures, the kinds of alteration in these details that result
from the use of other fixatives, and the nature of such
other optically recognized structures as the clefts of
Schmidt-~an~~~n and the nodes of Ranvier.

References

1. FERN~%CMO&, H.  13'mp. cell. Res., 1950, 1, 143.
2. NEWMAN, 5. B., B~YSKO, IV., and SWERDLOW, M. Science,
   1949, 110, 66.
3. Roean, Q. et al.  Biochim. Biophys. Beta, in press.