400 JAMES HILLIER 



by high melting point paraffin) , and a simple modification of a stand- 

 ard rotary microtome, succeeded in producing, routinely, sections 

 only 0.1 M thick and quite suitable for electron microscope studies (18). 



C. ELECTRON MICROSCOPES, AUXILIARY APPARATUS, 



AND TECHNIQUES 



1. Number of Electron Microscopes 



It has already l^een indicated that nearly any laboratory interested 

 in the heterogeneous microscopic structure of solid materials, regard- 

 less of their nature, can make profitable use of an electron micro- 

 scope. While it would appear that practically every scientific labora- 

 tory that in some way was interested in chemistry, physics, min- 

 eralogy, metallurgy, geology, many types of engineering, biology, 

 or medicine would have a need for an electron microscope, it is of 

 interest to note that the total number in the laboratories of the world 

 probably does not exceed 400, a number that is being increased at the 

 rate of roughly one per w^eek. 



In additi(^n to those already given, a very important factor limiting 

 the rate of growth of the use of the electron microscope is the shortage 

 of trained pers(jnnel. AVhile this shortage has existed for several 

 years in all fields of science, it has been particularly acute in the case 

 of electron microscopists. Most laboratories that have recognized 

 their need for an electron microscope have also realized that it will 

 be applicable to a number of the different problems being investigated 

 in their laboratories. At the same time, they have been aware that 

 it would be inefficient and uneconomical — not to mention vmsuccess- 

 ful — ^for all the individuals working on these problems to interrupt 

 work to learn the techniques of electron microscopy. It has been 

 shown to be much more satisfactory to set up the electron microscope 

 in a separate service group with its own trained personnel. This 

 results in a minimum requirement of at least one trained electron 

 microscopist for each instrument. Up to the present time, the 

 necessary training has been available only through actual experience 

 with the instrument in a laboratory using it. Since the adequate 

 training of a microscopist in this w^ay usually takes the better part of 

 two years, the instruments have been delivered at a much higher 

 rate than personnel to operate them have become available. This 

 situation should be remedied in the very near future, since a number 



