There was a pathologist, possibly from New York, who had examined hundreds if not thousands of corpses, and it was his medical opinion that the (heart?) blood of a person who has died in extreme agony separates into blood and blood plasma. Blood plasma, I read, makes up about 55% of total blood volume, and about 90% of blood plasma is water.
So I am taking it that both blood and water flowed from the wound to his heart, in quantities.
I’m not sure the following is any different from what the pathologist was saying. I’m not a physician, so I would not contest what he says, even if I might seem to.
My understanding is that a crucified person’s auxiliary breathing muscles would go into tetany after hanging for any significant period of time, thus requiring a great deal of difficulty in breathing due to the position of the person on the cross. Diaphragmatic breathing was difficult in any possible position the victim could attain. In attempting to avoid asphyxiation, the person would try to raise himself up so he could employ his chest muculature. But it was precarious, not to mention painful, because he could not fully straighten his legs. They would go into spasm and he would slump down again. The process would repeat, over and over, which is what made it such a terribly torturous way to die.
Eventually, the difficulty in breathing, elevated blood pressure and difficulties in returning blood through the heart (in which dehydration would also play a part) would cause ascites, which is the collection of serum in the interstitial space. That’s why people with congestive heart failure often have bloated-looking stomachs. Ultimately the person crucified would die of congestive heart failure. If the person’s legs were broken, it would accelerate the process because he could no longer raise himself up to breathe with his chest muscles and relieve stressed diaphragmatic breathing.
A standard Roman military killing technique was to stab a person through the diaphragm and into the heart with a blow from the side; the blade passing below the level of the rib cage near the sternum, through the diaphragm and into the heart with an upwart slant. In war, that blow was delivered with a short sword, and was immediately disabling and invariably deadly if done successfully. Roman soldiers were trained in anatomy and knew exactly how to inflict the various “field manual” wounds, of which there were several.
If a person with ascites is stabbed in that manner, whether by a sword in an eye-to-eye level encounter, or from somewhat below by a spear if one is somewhat elevated, watery serum will flow out copiously from the interstitial space and out the wound. Some blood will also flow, but if the person is already dead, most of the flow will be serum due to its ready availability to the wound site and the relatively greater pressure it is under.
Now, if gospel writers reported “blood and water” flowing from the wound, they had to know quite a bit about crucifixion even to invent the story, or they had to have seen it or been told of the events by an eyewitness. If they knew neither, they would have had no reason to expect serum (“water”) to have flowed from the wound. Given the knowledge of biomechanics at the time, no one would have thought to simply invent that detail out of the whole cloth.
I realize none of the above proves the veracity of the NT, and particularly not to one who wants to pick the NT apart for his own religious or non-religious purposes. But the account is biomechanically quite plausible; and, in itself, hardly demonstrates the falsity of the gospels.