Fernando de Castro (1896-1967) and the discovery of the arterial chemoreceptors
The last of Cajal's direct disciples cut the glossopharyngeal roots inside the skull of seventeen cats and three dogs, found the carotid body still innervated, and concluded in 1928 that it was a sensory organ built to taste the blood. That is the invention of chemoreception. The Nobel Prize for the reflex went to Ghent ten years later, while its author spent the war guarding the Cajal Institute.
Why this wins its question: The standard sentence is "the carotid body chemoreceptors, whose reflex Heymans described, winning the 1938 Nobel Prize", with de Castro reduced to a citation or dropped. This object reconstructs what he actually did and when: the 1926 paper and the two conclusions in it that were wrong, the anatomical reason they were wrong, the intracranial section in twenty animals that settled the question in 1928, and his own words proposing an organ that tastes the blood and a secretory intermediary between cell and nerve. It gives Heymans his due in the same breath — the stimulus and the reflex target were Ghent's work, not Madrid's — quotes the Nobel ceremony speech that named de Castro, and flags that the most eloquent source on his life is written from inside his own institute and family archive, which is why the war-cost claim is the weakest one here.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
Before de Castro the carotid body had no agreed identity: it had been called a small autonomic ganglion, a gland, a glomus and a paraganglion. Luschka in 1862 named it glandula intercarotica and described it as a gland with glandular tubes on the model of the adrenal; Julius Arnold in 1865 described instead a ball of convoluted vessels and named the structures glomeruli arteriosi intercarotici; Kohn in 1900 classed it as a paraganglion of the sympathetic system.
His first paper on the organ, in 1926, was stained by Cajal's reduced silver nitrate method and established that the parenchymatous cells are reached by fibres arriving through the carotid sinus nerve from the glossopharyngeal, directly, without an autonomic ganglion interposed — contrary to the rule then admitted for glands. The same paper drew two wrong conclusions, which the reviewing physiologists state plainly: he placed the trophic centres of those fibres in the brain stem, and he read their function as secretomotor.
The error had a cause that the review names, and it is not carelessness: de Castro's 1926 sections of the glossopharyngeal were made where the nerve leaves the skull, which is distal to the petrosal sensory ganglion, so both brain-stem and sensory fibres degenerated and the result was compatible with either reading. He was, in the authors' words, "strictly faithful describing his observations" and biased in the interpretation by the prevailing view that the organ was a gland.
The decisive experiment of 1928 was an intracranial one: he cut the roots of the ninth and tenth cranial nerves — occasionally also the eleventh — inside the skull, in seventeen cats and three dogs, and collected the nerves and the carotid bifurcation five to twelve days later. The carotid sinus nerve looked essentially normal and the cells of the organ remained innervated, which placed the cell bodies of those axons in the petrosal ganglion, a sensory ganglion, and not in the brain stem.
The conclusion he drew is the origin of the concept of chemoreception, and he stated it as a hypothesis rather than a discovery: "In sum, the Glomus caroticum is innervated by centripetal fibers, whose trophic centers are located in the sensory ganglia of the glossopharyngeal, and not by centrifugal [efferent] or secretomotor fibers as is the case for glands", and "As a plausible hypothesis we propose that the Glomus caroticum represents a sensory organ, at present the only one in its kind, dedicated to capture certain qualitative variations in the composition of blood."
He also proposed, in the same 1928 text, the mechanism now called a chemical synapse in the organ: the sensory fibre "would not be directly stimulated by blood, but via the intermediation of the epithelial cells of the organ, which, as their structure suggests, possess a secretory function which would participate in the stimulation of the centripetal fibers".
What de Castro did not have was the stimulus and the target of the reflex. Those were supplied almost immediately by the Ghent laboratory of Corneille Heymans, whose merit the reviewers state without qualification: the discovery of the qualitative changes in blood composition that the chemoreceptor cells detect, and the description of the lungs as the main target of the chemoreflex, published in 1930. Heymans received the Nobel Prize in Physiology or Medicine in 1938; de Castro did not share it.
The Nobel award ceremony speech itself credited the Spaniard. The review reproduces, as a footnote sourced to the Nobel Foundation's 1938 press page, Professor G. Liljestrand's words: "de Castro (1928) demonstrated that the anatomy of the glomus could no be compared to that of the suprarenal medulla. de Castro suggested that the glomus was an organ whose function was to react to variations in the composition of the blood … an internal gustatory organ with special 'chemo-receptors.' Heymans et al. (1930) undertook to find out whether these supposed chemo-receptors were responsible for the respiratory reflexes produced by modifications in the composition of the blood." The quotation is taken at second hand: the Nobel Foundation page was not reachable on the verification date, which is why this claim sits below the others.
He belonged to Cajal's laboratory not as a visitor but as its instructor: Cajal entrusted him with directing the technical training and research of the fellows who arrived at the Cajal Institute from the whole world between 1924 and 1932, among them Deszö Miskolczy, the future Nobel laureate Howard Florey, André Dewulf and the Uruguayan Clemente Estable. With Rafael Lorente de Nó he was, on this account, the last and youngest of Cajal's direct disciples.
The war interrupted the work at the moment it mattered. Fighting reached Madrid at the end of 1936 and de Castro, charged with protecting the equipment and collections of the Cajal Institute, was fully occupied for the almost three years of the Spanish Civil War in keeping the Institute from disappearing. The judgement that Heymans "took advantage of the opportunity and won the race" is the account of an author writing from inside the Instituto Cajal and from the family archive, and is reported here as his reading rather than as an established cause.
He returned to the international laboratory circuit only after the second war: his travel request granted by the Junta de Relaciones Culturales, he reached New York at the beginning of 1947 to work with Herbert S. Gasser and with Lorente de Nó and to learn electrophysiological recording, and he worked on the chemoreceptors and on the sensory and autonomic ganglia until his death in 1967.
His earlier ganglion work had an argumentative edge that is easy to miss. In describing the endings on the cells of the intercarotid gland he insisted, three or four times over, that the nerve endings do not penetrate the cytoplasm but remain external and adapt to the cell surfaces — a statement that only reads as trivial today, and which at the time was evidence for Cajal's neuron doctrine against the reticularists who held that neuronal cytoplasm formed a continuous syncytium.