Past exam of the medicine course of the University of Oxford / 1864 / Second examination / Forensic medicine and hygiene / 5 / Solution

An undecomposed infant with uniformly unaerated lungs provides evidence supporting absence of breathing, but a negative lung flotation test cannot establish with certainty that no breath was ever taken. The strength of the conclusion depends on the whole investigation.

First establish the circumstances of discovery, apparent maturity, preservation and any manipulation of the body. Reliable observations during and immediately after delivery would be particularly valuable, but none are supplied here and none should be invented. Record whether artificial respiration was attempted and whether putrefaction has begun. Both can affect the interpretation of gas in the lungs.

At examination, lungs that remain small, dense and unexpanded, rather than aerated and expanded, support the hypothesis of no established pulmonary ventilation. In the historical hydrostatic procedure, test the lungs in water, followed by individual lobes and representative pieces; record differences between regions. Uniform sinking in a fresh, unmanipulated body is more consistent with lack of aeration than a mixed result. Inspection and section of the tissue help distinguish an apparently unexpanded lung from one containing localized gas. This is a method of assembling evidence, not a claim that any particular infant in the question has those findings.

The logical limitation is essential. Breathing can have been brief or ineffective, and diseased or incompletely expanded lungs may sink despite prior life and breathing. A modern prospective autopsy study recorded four false-negative flotation results among 208 examined newborns: the lungs sank despite evidence of prior life. That observation disproves an absolute rule equating sinking with never having breathed; it is not a universal accuracy estimate for all forensic populations.^[ref]

Conversely, floating tissue need not prove spontaneous breathing: putrefaction or introduced air during artificial respiration may produce gas. Historical case-record research also documents why investigators combined the flotation result with the other findings and circumstances.^[ref]

Thus several concordant observations can justify the cautious opinion that no effective breathing has been demonstrated and that absence of breathing is the best-supported explanation. They do not justify certainty from a single negative test. Finally, the absence of breathing and the absence of every sign of life are different propositions: an assessment of live birth cannot simply be replaced by a test of lung buoyancy.