Applications of Electronics in Medicine 55 



electron microscope, the electrostatic electron microscope, the 

 scanning microscope, and the shadow electron microscope. 



The electron microscope is of value in the study of viruses, 

 bacteriophages, the combination of antibodies with flagellar and 

 somatic antigens, the structure of bacteria, organic chemistry, etc. 



The Cyclotron and Betatron 



Rutherford, twenty-six years ago, performed the first mutation 

 of one element into another, viz., nitrogen into oxygen, and 

 directed attention to the means of energizing particles to such 

 a degree as would enable them to penetrate the nuclear barrier 

 of the atom. J. H. Lawrence experimented with lower voltages 

 tuned to give the particles a series of pushes. Thus, the cyclotron 

 was brought into being — an instrument in which the particle is 

 kept moving in a circular path by a magnetic field, and inter- 

 mittently accelerated by an electrical field. These particles move 

 inside two hollow semicircular electrodes placed between the 

 poles of an electromagnet, and are accelerated by an oscillating 

 potential applied to the electrodes every time they cross the 

 central gap between them. The angular velocity of the particle 

 caused by the magnetic field is constant, but the successive 

 acceleration of its linear velocity, caused by the electrical field, 

 makes it move in an ever widening flat spiral. The ultimate 

 energy of the particle is limited only by the diameter of the 

 hollow electrodes. Experimenters in nuclear physics, in the last 

 ten years, had energies extending up to 16 million electron 

 volts available in the form of high-speed positive ions from the 

 cyclotron. 



The three major fields of biological study developed about 

 the cyclotron are : the use of a radioactive element to trace the 

 absorption, utilization, and excretion of its stable isotope by the 

 body in both health and disease ; the therapeutic effect of the 

 radiations emitted by radioactive substances internally admin- 

 istered ; and beams of both fast and slow neutrons are being 

 used in the treatment of cancer in a manner similar to X-rays 

 and y-rays in external therapy. 



