The self-selection tests were conducted with a single cage for each rat, equipped with up to 20 bottles and cylinders for liquids along with a number of food cups for solid nutrients. Each vessel contained a different nutritive substance, and the rat was free to choose among them. All substances were easily measured to determine what the rats ate. With these cages, Richter could examine the rat's ingestive regulatory functions in wild and laboratory specimens.
Rat Handling Aids
Many of the problems faced in the Psychobiology Laboratory were of a practical nature. How,
for example, was one to inject feisty wild rats, freshly culled from the streets of Baltimore?
Richter's typically inventive solution used the ribs from a broken umbrella with an old sock
stitched to the open end. Given the opportunity, feral rodents would dart into the sock, only to
shoot out the other end into the waiting conic cage. Squeezing down on the umbrella ribs
effectively immobilized the rat while conveniently exposing its body for different kinds of
Developed with Maurice Levine in the early 1930s, the dermometer was a small, portable
unit for measuring electrical skin resistance. Consisting of an ammeter, a voltmeter, two
potentiometers, and a battery, the dermometer replaced the string galvanometer that Richter had
been using for the same purpose. Because it was relatively small (about the size of a typewriter of
the same era), it could be carted around the hospital for use at the patient's bedside. Richter used
the test of electrical skin resistance to study sleep, mental disorders, and nerve function. During
the Second World War, Richter received several federal contracts to apply his dermometer to the
problem of nerve damage in servicemen. Late in the war, a smaller, improved dermometer was
issued to all Army neurosurgical services.