Hydrostatic Test (Raygat's Test / Lung Float Test)

Definition & Principle

Procedure (Step-by-Step)

1. Step 1 - Remove the "pluck": At autopsy, the lungs are removed intact with the bronchi, trachea, and larynx. A ligature is tied across the bronchi and the lungs are separated from other structures.
2. Step 2 - Whole lung test: Each lung is placed in a container of water.
   • Floats = positive (suggests respiration occurred)
   • Sinks = negative (suggests no respiration)
3. Step 3 - Cut lung test: Each lung is cut into 12-20 pieces (some sources say 15-20). Each piece is individually placed in water and observed for flotation.
4. Step 4 - Compression test: Floating pieces are:
   • First squeezed between thumb and index finger under water - observe if air bubbles escape
   • Then removed, wrapped in cloth, and squeezed firmly (or a weight placed on them) to expel tidal air
   • Pieces are placed back in water
5. Interpretation after compression:
   • Pieces continue to float = residual air present = respiration has occurred (liveborn)
   • Pieces sink after pressure = no residual air = respiration has NOT occurred (stillborn)
   • Some pieces float, others sink = feeble/partial respiration has occurred
6. Control: A small piece of liver is placed in water as a control.
   • Liver normally sinks. If the liver floats, it indicates putrefaction, and the entire test is invalidated.

Crepitance of Lungs (Gross Examination Findings)

Fallacies of the Hydrostatic Test

A. Expanded (respired) lungs may falsely SINK due to:

1. Disease - acute pulmonary edema, pneumonia, congenital syphilis
2. Atelectasis (failure of lung expansion):
   • Feeble respiratory effort - insufficient air entry
   • Complete absorption of air by blood if circulation continued after respiration stopped
   • Very feeble respiration where more air is expelled than inhaled
   • Obstruction by an alveolar duct membrane

B. Non-expanded (non-respired) lungs may falsely FLOAT due to:

1. Putrefactive gases - putrefied lungs are soft and greenish; gas bubbles under the pleura that can be moved with a finger stroke and collapse on pricking; body shows signs of decomposition
2. Artificial inflation - lungs may be inflated by blowing air through a tube/catheter into the trachea, or by mouth-to-mouth; in such cases:
   • Lungs are only partially inflated
   • Stomach may contain air but NOT the intestines
   • No mottled/marbled appearance
   • On section: little blood and no froth exudes
   • External cardiac massage and oxygen administration also negate the test
3. Trial breathing in utero - towards the end of pregnancy, some amniotic fluid moves in and out of the bronchial tree ("trial breathing"), causing some alveolar expansion in undoubted stillbirths

When the Hydrostatic Test is NOT Necessary

1. The fetus is a monster (congenital malformation incompatible with life)
2. The fetus is macerated or mummified
3. The fetus was born before 180 days of gestation (previable)
4. The stomach of the fetus contains milk (proves it was liveborn and fed)
5. The umbilical cord has separated and a scar has formed (proves postnatal survival)

Other Associated Tests for Liveborn Status

Medicolegal Value and Limitations

"This test is of no value whatsoever in forensic work" - primarily because:

• Any degree of decomposition invalidates it
• Resuscitation attempts (CPR, mouth-to-mouth) make evaluation impossible
• Lungs of undoubted liveborns who lived for days may sink
• Lungs of undoubted stillborns may float
• Intrauterine trial breathing can cause alveolar expansion in stillborns
• Histologically, it is not always possible to distinguish stillborn from liveborn lung tissue (Shapiro)

"At the present time, the authors place most reliance on the hydrostatic test. We determine if both lungs float in toto and then we attempt to float sections of the lungs. If all float, then in our opinion, the child most likely breathed and was, therefore, most likely alive" - provided there has been no resuscitation attempt and no decomposition. The liver is used as a marker for putrefaction; if the liver floats, the lung float results are negated.

• The Essentials of Forensic Medicine and Toxicology, 36th ed. (2026), pp. 426-427
• PC Dikshit Textbook of Forensic Medicine and Toxicology, p. 327
• Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, p. 470
• DiMaio's Forensic Pathology, 3rd ed., p. 305-306