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REPORT OF COMMISSION V GV—51 
grees of etching. Four electron micrographs from such a standard series are 
shown in Figure 3. 
Although the replica methods have had their greatest exploitation in elec- 
tron microscopy, they have also been applied profitably in studies made with 
the optical microscope (Refs. 7, 8, 9, 10). Negative surface replicas adequate 
for optical examination are very easy to prepare. Most of the techniques that 
are used parallel those employed in the preparation of specimens for electron 
microscopy, except that, inasmuch as visible light is much more readily trans- 
mitted by them, the films can be made thick enough so that they can be stripped 
manually from the surfaces with little difficulty. The simplest procedure con- 
sists in applying a strip of plastic sheeting under finger pressure to the surface, 
which has previously been wetted with a solvent for the plastic. The structural 
detail of the surface is thus imprinted into the superficially softened plastic, 
which then sets as the solvent evaporates. If cellulose acetate and acetone are 
used, a replica can be stripped in less than one minute. The optical micrographs 
in Figure 4 illustrate the type of pictures that can be obtained from metal- 
shadowed collodion and cellulose acetate replicas. 
The examples presented above demonstrate clearly that, even in the absence 
of stereoscopic pairs of photographs, much can be learned about the third 
dimension of surface structures from single micrographs of shadowed replicas. 
Experience has shown that the information thus derived is adequate for the 
purposes of most investigations. At the electron microscopic level, the procedure 
generally followed in surface studies has been to make single photographs from 
shadowed replicas routinely, and stereo pairs from unshadowed replicas in the 
event of confusion in interpretation or when the tridimensional effect is not 
sufficiently pronounced. 
REFERENCES 
1. Wyckoff, R. W. G., Electron Microscopy. Interscience, New York, 1949. 
2. Scott, D. B., “Recent Contributions in Dental Histology by Use of the Electron Microscope.” 
Internat. Dental J., 4: 64-95 (1953). 
3. Helmcke, J. G., Atlas des Menschlichen Zahnes im Elektronenmikroskopischen Bild, Transmare 
Photo G.M.B.H., Berlin-Wilmersdorf, 1953. 
4. Helmcke, J. G., “Theorie und Praxis der Elektronenmikroskopischen Stereoaufnahmen." 
Optik, 11: 201—225 (1954). 
. Scott, D. B., and Wyckoff, R. W. G., “Electron Microscopy of Tooth Structure by the Shad- 
owed Collodion Replica Method." Public Health Rep., 62: 1513-1516 (1947). 
6. Scott, D. B., and Wyckoff, R. W. G., “Carbon Surface Replicas for Electron Microscopy and 
Electron Diffraction.” J. Royal Microscopical Soc., in press. 
. Scott, D. B., and Wyckoff, R. W. G., *Shadowed Replicas of Tooth Surfaces." Public Health 
Rep., 61:697—700 (1946) 
8. Scott, D. B., and Wyckoff, R. W. G., 'Shadowed Replicas of Ground Sections through Teeth." 
Public Health Rep., 62: 422-425 (1947). 
9. Scott, D. B., and Wyckoff, R. W. G., “Metal Shadowing for the Optical Microscopy of Certain 
Tissues.” Am. J. Clinical Pathology, 19: 63-66 (1949). 
10. Scott, D. B., “Microscopic Studies of Dental Tissues. II. Optical Microscopy of Tooth Sur- 
faces.” Oral Surgery, Oral Medicine, and Oral Pathology, 5: 638-645 (1952). 
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