One of the most gratifying applications of an important technique of submarine detection is in the exploration of the human body. Our readers are familiar with the principles of sonar where sound waves are sent out in water and the echoes then indicate submerged objects. Various methods of pulsing, scanning, and displaying these sound waves are used to detect submarines, map ocean floors, and even communicate under water. In medicine the frequencies are much higher, transducers and the sonar beams themselves are much smaller, and different scanning techniques may be used, but the principles involved are the same as in sonar.

Because the body contains so much liquid, transmission of ultrasonic signals proceeds fairly well in muscles and blood vessels. Bones and cartilage transmit poorly and tend to reflect the ultrasonic signals. Based on this phenomenon, a number of investigators have used this method to ``look through'' human organs. A good example of the results obtainable with ultrasonic radiation is contained in papers presented by Dr. G. Baum who has explored the human eye. He can diagnose detachment of the retina where conventional methods indicate blindness due to glaucoma. The method used to scan the eye ultrasonically is illustrated in Fig. 6. The transducer is coupled to the body through a water bath, not shown. For display, Dr. Baum uses a portion of an ** f, an airborne radar indicator, and then photographs the screen to obtain a permanent record.