As a child Haller was so sickly that he was unable to amuse himself with the sports and games common to boys of his age, and so passed most of his time poring over books. When ten years of age he began writing poems in Latin and German, and at fifteen entered the University of Tubingen. At seventeen he wrote learned articles in opposition to certain accepted doctrines, and at nineteen he received his degree of doctor. Soon after this he visited England, where his zeal in dissecting brought him under suspicion of grave-robbery, which suspicion made it expedient for him to return to the Continent. After studying botany in Basel for some time he made an extended botanical journey through Switzerland, finally settling in his native city, Berne, as a practising physician. During this time he did not neglect either poetry or botany, publishing anonymously a collection of poems.

In 1736 he was called to Gottingen as professor of anatomy, surgery, chemistry, and botany. During his labors in the university he never neglected his literary work, sometimes living and sleeping for days and nights together in his library, eating his meals while delving in his books, and sleeping only when actually compelled to do so by fatigue. During all this time he was in correspondence with savants from all over the world, and it is said of him that he never left a letter of any kind unanswered.

Haller's greatest contribution to medical science was his famous doctrine of irritability, which has given him the name of "father of modern nervous physiology," just as Harvey is called "the father of the modern physiology of the blood." It has been said of this famous doctrine of irritability that "it moved all the minds of the century - and not in the departments of medicine alone - in a way of which we of the present day have no satisfactory conception, unless we compare it with our modern Darwinism."[1]

The principle of general irritability had been laid down by Francis Glisson (1597-1677) from deductive studies, but Haller proved by experiments along the line of inductive methods that this irritability was not common to all "fibre as well as to the fluids of the body," but something entirely special, and peculiar only to muscular substance. He distinguished between irritability of muscles and sensibility of nerves. In 1747 he gave as the three forces that produce muscular movements: elasticity, or "dead nervous force"; irritability, or "innate nervous force"; and nervous force in itself. And in 1752 he described one hundred and ninety experiments for determining what parts of the body possess "irritability" - that is, the property of contracting when stimulated. His conclusion that this irritability exists in muscular substance alone and is quite independent of the nerves proceeding to it aroused a controversy that was never definitely settled until late in the nineteenth century, when Haller's theory was found to be entirely correct.

It was in pursuit of experiments to establish his theory of irritability that Haller made his chief discoveries in embryology and development. He proved that in the process of incubation of the egg the first trace of the heart of the chick shows itself in the thirty-eighth hour, and that the first trace of red blood showed in the forty-first hour. By his investigations upon the lower animals he attempted to confirm the theory that since the creation of genus every individual is derived from a preceding individual - the existing theory of preformation, in which he believed, and which taught that "every individual is fully and completely preformed in the germ, simply growing from microscopic to visible proportions, without developing any new parts."

In physiology, besides his studies of the nervous system, Haller studied the mechanism of respiration, refuting the teachings of Hamberger (1697-1755), who maintained that the lungs contract independently. Haller, however, in common with his contemporaries, failed utterly to understand the true function of the lungs. The great physiologist's influence upon practical medicine, while most profound, was largely indirect. He was a theoretical rather than a practical physician, yet he is credited with being the first physician to use the watch in counting the pulse.