Since the theme of this work borders at least on the sphere of psycho-analysis, it is interesting to observe what light behaviouristic analysis throws upon phenomena which bear a certain relation to those familiar to the psycho-analyst. It stands to reason that the method differs fundamentally from psycho-analysis. The authors have focussed their studies upon those aspects of behaviour which can be examined by physiological instrumentation—'without dependence upon psychological interpretation'.

The nervous disturbance studied by the authors (and their predecessors) made its appearance in the course of work undertaken to determine the differentiating ability of the experimental sheep under various conditions. Using the conditioned reflex method, they attempted to force the animals to distinguish, for example, between a rapidly beating metronome and a slowly beating one. It was observed that, when the problem became too difficult for the animal to solve (that