TabulaThe body, as it was written.

A tour · 2 plates

The hidden vessels

Some parts of the body are hard to miss. The lymphatic system is easy to miss: its vessels are thin, usually carry clear fluid and collapse after death. This short tour follows how it was found, and found again. In 1622 Gaspare Aselli opened a dog that had just eaten and saw white vessels full of chyle running from the gut. He assumed they led to the liver, as Galen's system required.1 Jean Pecquet showed in 1651 that they do not.2 In 1787 Paolo Mascagni described lymphatic vessels in the dura mater, the tough outer covering of the brain, but the observation was largely overlooked.3 Later work fed a consensus that the brain has no lymphatics at all.4 In 2015 two groups reported the vessels again, and the news spread as a discovery.5 Two plates, almost four centuries apart: one structure hidden physically, and one hidden by what everyone was sure of.

▶ Play this tour Read the long version

  1. Tab. XV: The milky veins (1622 (seen) · 1627 (published))
  2. Tab. XXV: Discovered in 2015, described in 1787 (2015 (and 1787))

Sources for this introduction

  1. Aselli saw the lacteals in 1622 while vivisecting a dog that had been fed shortly before, and believed they carried chyle to the liver.

    • Gaspare Aselli, De lactibus sive lacteis venis. 1627. Milan. primary
    • Royal College of Surgeons of England, Library, Gaspare Aselli, De lactibus sive lacteis venis (1627). n.d.. Link · Archive scholarly
    • Jeremy M. Norman (HistoryofMedicine.com, Garrison-Morton), Aselli, De lactibus. n.d.. Link · Archive secondary

  2. Jean Pecquet's discovery of the thoracic duct, published in his Experimenta nova anatomica (1651), showed that the lacteals do not lead to the liver.

    • Jean Pecquet, Experimenta nova anatomica. 1651. primary
    • Jeremy M. Norman (HistoryofMedicine.com, Garrison-Morton), Aselli, De lactibus. n.d.. Link · Archive secondary
    • Royal College of Surgeons of England, Library, Gaspare Aselli, De lactibus sive lacteis venis (1627). n.d.. Link · Archive scholarly

  3. Paolo Mascagni's atlas of the lymphatic system, published in 1787, described lymphatics in the cerebral dura mater; it was written in Latin and largely overlooked.

    • Paolo Mascagni, Vasorum lymphaticorum corporis humani historia et ichnographia. 1787. Siena. primary
    • (review, PubMed Central), So You've Made a Novel Discovery: The History of Our Knowledge of Central Nervous System Lymphatics May Change Your Mind. n.d.. Link · Archive scholarly · details pending
    • Frontiers in Immunology (review), [Review of meningeal lymphatics including their history, article 3043]. 2019. Link · Archive scholarly · details pending

  4. Later nineteenth-century work, notably by Key and Retzius, influenced the long-standing view that the brain lacks lymphatic drainage.contested

    Historians differ on how much one work shaped the textbook consensus.

    • Axel Key, Gustaf Retzius, Studien in der Anatomie des Nervensystems und des Bindegewebes. 1875–1876. Stockholm. primary
    • (review, PubMed Central), So You've Made a Novel Discovery: The History of Our Knowledge of Central Nervous System Lymphatics May Change Your Mind. n.d.. Link · Archive scholarly · details pending

  5. In 2015 two independent groups, Louveau and colleagues in Nature and Aspelund and colleagues in the Journal of Experimental Medicine, reported lymphatic vessels in the meninges.

    • A. Louveau et al., Structural and functional features of central nervous system lymphatic vessels. 2015. Nature 523. primary
    • A. Aspelund et al., A dural lymphatic vascular system that drains brain interstitial fluid and macromolecules. 2015. Journal of Experimental Medicine 212. primary
    • (review, PubMed Central), So You've Made a Novel Discovery: The History of Our Knowledge of Central Nervous System Lymphatics May Change Your Mind. n.d.. Link · Archive scholarly · details pending