406 JAMESHILLIER 



and studied objectively, many hundreds of exposures. Too much 

 emphasis cannot be placed on the necessity of taking large numbers 

 of exposures and correlating the appearance of the image at very high 

 magnifications with the mode of operation of the instrument. It is 

 the opinion of the writer that the only really essential prerequisites 

 to the training of an electron microscopist is that he have sufficient 

 natural aptitude for the handling of scientific equipment plus the 

 basic knowledge of the optics of any microscope. Training in physics 

 and electronics will be helpful but only in that such knowledge will 

 permit him to discover more rapidly the cause of the improper func- 

 tioning of any part of the instrument. 



5. Skill Involved in Preparation of the Specimen 



If a worker considers the possibility of utilizing an electron mi- 

 croscope in the investigation of the structure of a material he is 

 studying, it is to be presumed that that worker is quite familiar 

 with many properties of that material. Because of this it is very 

 difficult to differentiate between the skill required by the research 

 worker in the normal execution of his investigation and that required 

 to prepare that specimen in a form suitable for electron microscopy. 



There are, however, a few technical aspects of the preparation of 

 electron microscope specimens that may require special skill. For 

 instance, such a preparation almost always involves the handling 

 of very thin film, which must be produced and mounted on wire 

 screens or apertured discs. The specimen must be manipulated in 

 such a way that ultimately it is present on this film and must be thin 

 and free of extraneous materials. Fortunately, many satisfactory 

 techniques for handling these materials have been worked out and 

 are described in the literature. None of them is as difficult as might 

 be expected. Beyond this the research worker is simply handling, in 

 perhaps a somewhat different manner, material with which he is 

 familiar. One might consider, for example, the case of a bacteriolo- 

 gist. He is quite familiar with the methods of making films and of 

 fixing and staining the organism for light microscope examination. 

 Actually, he can carry out identical manipulations for the electron 

 microscope preparation with the one exception that he covers the 

 microscope slide with a thin plastic film that is later to become his 

 supporting membrane. After he has completed his manipulation, 

 he floats this membrane off the glass slide and onto the surface of 

 water and picks it up on a wire screen. If, as he would most likely 



