Breuer, working for Ewald Hering at the military medical school in Vienna, was the first to demonstrate the role of the vagus nerve in the reflex nature of respiration.

This was different from previous physiological belief, and changed the way scientists considered the relationship of the lungs to the nervous system.

[2] Independent of each other[3] in 1873, Breuer and the physicist and mathematician Ernst Mach discovered how the sense of balance (i.e. the perception of the head's imbalance) functions: that it is managed by information the brain receives from the movement of a fluid in the semicircular canals of the inner ear.

(the case pseudonym of Bertha Pappenheim), a woman suffering from "paralysis of her limbs, and anaesthesias, as well as disturbances of vision and speech".

Ernest Jones recalled, "Freud was greatly interested in hearing of the case of Anna O, which ... made a deep impression on him";[6] and in his work of 1909, Five Lectures on Psycho-Analysis, Freud stated, "I was a student and working for my final examinations at the time when ... Breuer, first (in 1880-2) made use of this procedure ... Never before had anyone removed a hysterical symptom by such a method.

[8] Louis Breger has observed that in the Studies, "Freud is looking for a grand theory that will make him famous and, because of this, he is always fastening on what he thinks will be a single cause of hysteria, such as sexual conflict...Breuer, on the other hand, writes about the many factors that produce symptoms, including traumas of a variety of kinds.