Mechanism of the brain.

This is a black and white, silent film, that explores the role the brain and nervous system play in behaviour. In doing so it also attempts to show the difference between conditioned and unconditioned responses in animals and humans. It begins by briefly examining behaviour in humans and animals, exploring how as humans develop their behaviour becomes more complex thus separating them from animals. Using annotated diagrams the film explains how behaviour is the result of the activity of the nervous system in which nervous tissue receives and transmits irritation. Footage of frogs being tested with irritants is used to demonstrate this. Absolute reflexes are then examined and attention is paid on absolute food reflex in dogs with footage of experiments observing mastication and secretion of saliva. This is then compared with conditioned reflexes. Diagrams are used to show how if two brain centres are stimulated simultaneously then a connection between the two is built and "an irritation of one centre causes that of the other". We are shown how the unconditioned production of saliva at the sight or smell of food can be conditioned to appear at the sound of a metronome. This is used to illustrate "the basis of the nervous activities of animals is the inborn relation of the animal to its environment". This idea is developed and the film shows how reflex actions can be produced when a stimulus (irritant) is removed. Relationship of animals and men to their environment is explored through more elaborate tests with footage of a monkey reacting to variations of the same stimuli, including different coloured discs and a metronome set at different tempos. This illustrates "a more finely adjusted accommodation to living conditions". The brains governance on behaviour and the role of different areas of the brain are then demonstrated through the behaviour of dogs and monkeys who have had parts of their brains removed. We see tests on children by Prof. Krasnogorski, indicating that "absolute reflexes, as well as conditioned reflexes, form the basis of the behaviour not only of animals but of men". Material of humans with underdeveloped or damaged brains is shown to illustrate the affect the brain has on human behaviour. The film concludes with the assertion that "absolute and conditioned reflexes form the basis of the behaviour of men and animals" and examples of behaviour in different stages of human development are used to show the development of human behaviour.