This book contains an excellent account of a method employed by experimental psychology. The work described has been published from time to time in separate papers and is now collected into one volume. Professor Maier acknowledges the difficulties of comparing the results of animal experimentation and those of clinical research, but he believes this to be a legitimate procedure if one accepts that the basic principles of mental functioning are not specific for a species but apply consistently throughout the animal kingdom.

Rats were trained in discrimination problems and then placed in a frustrating situation, i.e. they were faced with an insoluble problem from which there was no escape. After the initial efforts the animals generally refused to make further attempts at solving the problem. To overcome this difficulty