Effetto Jet

LE RISULTANZE MEDICO-LEGALI DELL'HOUSE SELECT COMMITTEE OF ASSASSINATIONS (1978): IL MOVIMENTO INDIETRO DELLA TESTA DI KENNEDY PRODOTTO DA UNA REAZIONE NEUROMUSCOLARE E DALL'USCITA IN AVANTI DI MATERIA CEREBRALE, O DALLA COMBINAZIONE DI QUESTI DUE ELEMENTI


EVALUATION OF THE MEDICAL, PATHOLOGICAL AND RELATED EVIDENCE PERTAINING TO THE DEATH OF PRESIDENT JOHN F. KENNEDY (BY THE FORENSIC PATHOLOGY PANEL)

o Michael M. Baden, M.D., Chairman of the Panel, Chief Medical Examiner, New York City, N.Y.
o John I. Coe, M.D., Chief Medical Examiner, Hennepin County, Minn.
o Joseph H. Davis, M.D., Chief Medical Examiner, Dade County, Miami,
o George S. Loquvam, M.D., Director, Institute of Forensic Sciences, Oakland, Calif.
o Charles S. Petty, M.D., Chief Medical Examiner, Dallas County, Dallas, Tex.
o Earl F. Rose, M.D., LL.B., Professor of Pathology, University of Iowa, Iowa City, Iowa
o Werner V. Spitz, M.D., Medical Examiner, Detroit, Mich.
o Cyril H. Wecht, M.D., J.D., Coroner, Allegheny County, Pittsburgh,
o James T. Weston, M.D., Chief Medical Investigator, School of Medicine, University of New Mexico, Albuquerque, N. Mex. second structure.
o Another consideration about missile wounds that has been emphasized by others(85) is the relatively short time that a missile is actually moving through tissue, usually less than a thousandth of a second. A bullet of 150-F rains weight, passing through 8 inches of tissue, entering at 2,000 feet per second (approximately the velocity of the 6.5 millimeter Mannlicher-Carcano bullet) and exiting at 1,000 feet per second will pass through the body in 0.00045 second and impart to the tissue 998 foot-pounds of energy, the work equivalent of more than 4,100 horse power. This energy transfer produces a temporary cavity as described earlier, which actually develops after the bullet has passed through the tissue. Accordingly, a bullet can pass through a head and be about 100 feet further along before a photograph reveals the explosive destruction of the head. This also explains the presence of entry and exit bullet holes in bones and tissue even though the skull is extensively fragmented or blown apart by the subsequent formation of the temporary cavity. The velocity of the outward-moving tissue particles may be only 125 feet per second, far less than the 1,000 to 2,000 feet per second velocity of the bullet projectile. Thus, when the Zapruder film reveals the explosion of the skull, the bullet had already passed through.
o Finally, the panel members also discussed their experiences with the explosive effects of shotgun and, to a lesser extent, military rifle wounds to enclosed portions of the body such as the head. Rarely has any member observed photographs documenting the reactions of victims' bodies to being shot, although crime scene reconstruction has often enabled panel members to establish body position prior to the shooting. The panel members have critically evaluated the observations of Alvarez (86) and the physical principles he considers in explaining the President's head movements in the Zapruder film. The panel members took note of the differences between the missile and targets (melons) in Alvarez's work and the missile and targets in this homicide. The work of Lattimer and associates,(87) which addressed some of these differences by using a weapon and missiles similar to those used in the Kennedy assassination and which attempted to duplicate the injury pattern on skulls, was also critically reviewed, as were studies by Dr. John Nichols. (88)
o The panel members agree that the exit wound of a missile seriously deformed by initial penetration of the skull might be considerably larger than the entrance defect and that the forces related to yaw and the large temporary cavity created by the missile would usually be transmitted fairly equally throughout a closed space such as the skull. The larger exit defect in the front of the skull would theoretically permit greater exodus of tissue under pressure, and a resulting backward movement of the head could occur.
o The panel is aware of the time interval between the backward motion of the President's head and the earlier, slight forward motion, possibly caused by the initial missile impact and transfer of energy to the head as recorded in frames 313-314 of the Zapruder film. The panel further recognizes the possibility of the body stiffening, with an upward and backward lunge, which might have resulted from a massive downward rush of neurologic stimuli to all efferent nerves (those which stimulate muscles). The disparity in mass and strength between those muscles supporting the body on the back (dorsal surface) of the spine and those muscles on the front (ventral) surface could account, at least partially, far this type of motion, although it would be reasonable to expect that all muscles would be similarly stimulated.
o The panel suggests that the lacerations of a specific portion of the brain--the cerebral peduncles as described in the autopsy report(89)--could be a cause of decerebrate rigidity, which could contribute to the President's backward motion. Such decerebrate rigidity as Sherrington (90) described usually does not commence for several minutes after separation of the upper brain centers from the brain stem and spinal cord. It is, however, most intense in those muscles which normally counteract the effects of gravity.
o The panel is also aware of possible effects on motion that could be caused by the moving car within which the President sat.
o The panel concludes that the backward movement of the head following its forward movement occurred after the missile had already exited from the body and had created a large exit defect in the skull, and that it was most probably due to a reverse jet effect, or a neuromuscular reaction, or a combination of the two. The short interval between the two motions supports this explanation.
o One panel member, Dr. Wecht, suspects that the backward head motion might be explained by a soft-nosed bullet that struck the right side of the President's head simultaneously with the shot from the rear and disintegrated on impact without exiting the skull on the other side. The remaining panel members take exception to such speculation, since they are unaware of any missile with such capabilities. Further, the X-rays taken prior to the autopsy show no evidence of a second missile, nor do the photographs of the head and brain show evidence of any injury to the left side.