200 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
of the cells on potassium tellurite chocolate agar. From this the 
experimenters were able to deduce that tellurium metal occurs in the 
form of needles and is the cause of the black color, and that this reac- 
tion occurs within the cells since the crystals have never been observed 
to lie totally outside the cell wall, although at times there is some 
distortion of the wall. 
The electron microscope also affords such study and observation 
as that carried out by Dr. W. M. Stanley, of the Rockefeller Institute 
of Medical Research, and Dr. Thomas F. Anderson in their recent 
investigation of plant viruses. By means of electron micrographs, 
they were able to judge the exact manner and extent of attack made 
on the tobacco mosaic virus by the protein antibodies in the blood 
stream of rabbits in which an artificial immunity to the virus had been 
produced. 
Structures like that of the spirochete of Weil’s disease, typhoid 
flagella, unusual internal structure of pertussis organisms, tubercle 
bacilli, the isolation and recognition of the influenza virus, the spores 
of trychophyton mentagrophytes, Spirochaeta pallida with its accom- 
panying flagellar appendages, and colloidal particles are but a few 
of the interesting revelations of the electron microscope for medical 
science. Industrial science, too, has found this new research tool of 
great value in the study of metals, alloys, and plastics, as well as in 
the study of size, shape, and distribution of particles in chemical com- 
pounds and elements. 
The electron microscope herein described is that manufactured by 
the Radio Corporation of America. There are, of course, variations 
in construction of the different instruments of this kind but all types 
are built along similar lines and upon the same general principles. 
In the electron microscope there is some aberration plus the additional 
disadvantages of having the specimen in a vacuum, not to mention the 
probable protoplasmic changes induced by the terrific bombardment 
of electrons, and finally, what is perhaps the greatest disadvantage 
insofar as medical science is concerned—that of being unable to view 
living organisms. Nevertheless, the disadvantages of the microscope 
are far overshadowed by its increased resolving and magnification 
powers which have combined to make it an invaluable research tool. 
RESOLUTION AND MAGNIFICATION OF ORDINARY MICROSCOPE 
We have stated that the resolving power of the ordinary light 
microscope is restricted to between 1,600 and 2,500 diameters and 
that of the ordinary ultramicroscope to between 2,500 and 5,000 
diameters, resolution in any microscope being the ability of the in- 
strument to reveal the most minute of component parts of a specimen 
so that each may be seen as a distinct and separate image. For in- 
