n 1904 Charles Sherrington, then professor of physiology at Liverpool, gave the Silliman lectures at Yale. Published two years later, they became the book that taught physiologists to think of the nervous system as a machine for combining reflexes into behaviour (Sherrington, C. S., 1906).

what it is, and where to read it

Ten lectures on spinal reflexes in the cat and dog: how they are excited, inhibited, timed and combined. The book is in the public domain and scanned in full at the Internet Archive.

what it says

Reflexes are not isolated; they compete for the same motor paths, a "final common path", and the nervous system resolves the competition by excitation and inhibition. Sherrington locates the decisive events at the junctions between neurons, which he had named in 1897. In the book he explains the word:

“In view, therefore, of the probable importance physiologically of this mode of nexus between neurone and neurone it is convenient to have a term for it. The term introduced has been synapse.”
— Sherrington 1906, p. 17

what's contested

In 1906 the junction was an inference. Golgi, accepting the Nobel Prize that year alongside Cajal, still argued that nerve cells are continuous (Nobel Prize Outreach, 1906). Sherrington sided with Cajal, on physiological grounds: conduction through a reflex is slower, one-way and more fatigable than along a nerve, which suggested a different kind of place in between. Electron microscopes settled the anatomy only in the 1950s. Whether transmission at the gap is chemical or electrical, soup or sparks, was argued for decades after (Loewi, 1921); both kinds turned out to exist.

methodological critiques

The evidence was behavioural: what a decerebrate or spinal animal's limbs did under stimulation. Nothing was recorded from a single cell. Critics then and since have noted the leap from reflex arcs to "integration" of the whole animal, a word the book uses more than it defines.

later reception

Sherrington shared the Nobel Prize in 1932 with Edgar Adrian. His students and successors, among them John Eccles, measured the synaptic events he had inferred. The idea of the synapse as the adjustable element, the place where learning lives, runs through Hebb to the weights of every artificial network.

in the tour: the room called "The gap" has a placard called "Soup or sparks" ···

References

1. Sherrington, C. S. (1906). The Integrative Action of the Nervous System. New York: Charles Scribner's Sons; New Haven: Yale University Press. The Silliman lectures of 1904. Public domain. archive.org/details/integrativeactio00sher
2. Nobel Prize Outreach (1906). The Nobel Prize in Physiology or Medicine 1906: Camillo Golgi and Santiago Ramón y Cajal. Prize summary page. www.nobelprize.org/prizes/medicine/1906/summary/
3. Loewi (1921). Über humorale Übertragbarkeit der Herznervenwirkung. Pflügers Archiv für die Gesamte Physiologie des Menschen und der Tiere. doi:10.1007/bf01738910
4. Hebb, D. O. (1949). The Organization of Behavior: A Neuropsychological Theory. New York: Wiley.

see also