Definition
A medical-forensic examination of fetal lung tissue used to determine whether a child was born alive or dead. The test — also called the hydrostatic lung test — works on the principle that lungs which have never drawn breath are dense and airless, while lungs that have inflated with air retain buoyancy. The examiner removes the lungs from the body and submerges them in water: lungs that sink indicate the child was stillborn; lungs that float indicate the child breathed and was therefore born alive.
The docimasia pulmonum was introduced as evidence primarily in infanticide prosecutions, where the central legal question was whether the infant had achieved live birth — a prerequisite to homicide liability under common law. It represents one of the earliest systematic applications of medical science to courtroom fact-finding.
Common Confusion
The test's apparent simplicity masked serious evidentiary problems that courts and medical witnesses debated for well over a century. Putrefaction produces gases that cause lungs to float even when the child never breathed, generating false positives. Conversely, partial respiration, premature birth, or diseased lung tissue could produce ambiguous or misleading results. The binary sink-or-float framing presented to juries often obscured what medical witnesses understood to be a probabilistic and conditional finding. Researchers working with historical trial records should not assume that a floating-lung result was treated as conclusive proof of live birth; the weight given to the test varied considerably by era, jurisdiction, and the sophistication of the presiding court.
Why It Matters in Research
This term is encountered almost exclusively in historical legal materials — primarily infanticide prosecutions, medical jurisprudence treatises, and coroner's inquest records from roughly the late seventeenth through the early twentieth centuries. It is rare in modern legal literature because the docimasia pulmonum has been superseded by more reliable forensic pathology techniques.
Several research traps warrant attention:
Terminology inconsistency. The same test appears in historical sources under multiple names: hydrostatic test, hydrostatic lung test, lung flotation test, and the Latin docimasia pulmonum. A corpus search on any single term will miss sources using the others. Cross-searching all variants is essential for comprehensive retrieval.
Evidentiary weight shifts over time. Early modern courts often treated a floating result as near-conclusive. By the mid-nineteenth century, medical and legal opinion had fragmented substantially, with leading medical jurists publicly challenging the test's reliability. Researchers reading historical opinions must situate the court's treatment of the evidence within this evolving professional consensus — a floating lung meant something different to an 1820 court than to an 1880 court.
Infanticide doctrine connection. The test's legal significance is inseparable from the common law definition of live birth and the specific elements of infanticide as a distinct statutory offense in English and many American jurisdictions. Sources on docimasia pulmonum will almost always sit adjacent to materials on concealment of birth statutes, which often created a lesser offense precisely because live birth was so difficult to prove.
Medical jurisprudence as a genre. The primary legal-adjacent sources are not law reviews but medical jurisprudence treatises — works by Taylor, Beck, Casper, and their successors — which were themselves frequently cited in court and commentary. These treatises are the best secondary sources for understanding how the test was presented to legal audiences.
Historical Dictionary Support
Black's Law Dictionary (2nd Ed.) provides the core definition with reasonable accuracy: the hydrostatic test, immersion of fetal lungs in water, sinking indicating no prior inflation and floating indicating prior breathing. The entry is brief and clinical, presenting the test as more settled than the historical medical literature warranted.
What Black's does not capture is the significant nineteenth-century controversy over the test's reliability. Medical jurists of the period — including Alfred Swaine Taylor, whose works were widely cited in Anglo-American courts — acknowledged that decomposition, accidental artificial respiration, and pulmonary disease could all confound results. This professional skepticism appears in the treatise literature but is absent from the dictionary entry, which gives the impression of a more definitive diagnostic tool than practitioners actually possessed.
No other source dictionary in the current Law Mind corpus carries an entry for this term. Researchers requiring fuller treatment should consult period medical jurisprudence treatises directly.
Jurisdictional Note
The test was used in both English and American courts, with English infanticide prosecutions generating the larger body of reported cases. American jurisdictions varied in how receptively courts treated floating-lung testimony, partly tracking regional access to trained medical witnesses. Scottish courts developed a parallel but distinct forensic tradition. Researchers working across these jurisdictions should not assume uniform evidentiary treatment.