Archive file# r102099a
donated by L. Savage
An Essay on Vampire Biology
Originally posted to the VAMPYRES list by Javelina
Before speculating on any specific pathogens capable of producing a
condition akin to vampirism, I wish to post an old line of reasoning on how
vampires manage to survive on a diet which contains so much water and so
Speculation on the subject of the dietary requirements of vampires must
first deal with what the blood is actually being used for. Some fiction,
including Elrod's novels, seems to assume that it is for circulatory
purposes. I am inclined to doubt this, in view of the general agreement
that hose who walk by night need not breathe. If the lungs are not being
ventilated, the purpose of blood circulation to the tissues seems
questionable at best.
Assuming that blood is being digested seems much more reasonable. It
raises, however, energetic issues. Blood is an awkward material to make a
living from. Vampire bats do this, but they have very little safety margin.
A bat that cannot feed on one night stands a strong chance of starving to
death before the next night. They also consume large fluid volumes
relative to their own body size.
Assuming first a digestive system operating after the pattern of living
animals, breaking down complex organic molecules to carbon dioxide and
water, one can do an interesting theoretical investigation of the energy
The recommended daily minimum caloric intake for a young adult male is
asserted by the relevant government agencies to be in the neighborhood of
2800 nutritionists calories (kcals to a physicist or biologist) per day.
This is alleged to be sufficient for minimal maintenance, not heavy labor.
Like most such figures, the adult in question is assumed to be the
stereotypical 70 kilograms, North American.
A mammal digesting protein obtains about 4.8 kcals from one gram (dry
weight!) of protein. The constituents of blood are almost entirely
proteinaceous, so it is convenient to use this value. To obtain 2800
kcals, then, necessitates the consumption of 583 grams dry protein per day.
I have been unable to obtain a lumped value for the total dry matter
present in a given volume of mammalian blood, but a convenient reference
tome (Altman and Dittmer; Biology Data Book) asserts that the concentration
of hemoglobin in human blood is 150 dry grams per litre. Yes, litre.
Because human blood cells do not accomplish much except hemoglobin
packaging, it is not unreasonable to take the 150 g per litre figure as the
total protein content.
The previous two paragraphs imply, then, that 583/150 =3.9 liters of blood
are required to meet human-level metabolic requirements.
I have a considerable distaste, for the above calculation. At most
generous estimate, a second and indubitably human adult will have a total
blood volume approximating 10% of his body weight .. let us say seven
kilograms. Seven litres, then. Mammals cannot survive the catastrophic
loss of more than about 30-40 percent of their total blood volume, that
being a maximum of 2.8 liters from the above 7 liter scenario. The loss of
20% of blood volume is almost invariably survivable, meaning that a loss of
1.4 litres would not be fatal, though the impact would be substantial and
unpleasant. All this suggest that IF mammalian energetic constrain the
obligately nocturnal readers of this list, they must be feeding on three
people a night. (The annual number of unsolved murders in the country,
high as it is, is not high enough to support the obvious possibility.)
A more reasonable (but not, I think, the most pleasing) suggestion would be
that the energetic model to examine is not that of mammals, but of
reptiles. The profligate habit of maintaining an elevated body temperature
imposes a tremendous cost on those of us silly enough to do so. As a very
rough approximation, a reptile has energy demands one tenth those of a bird
or mammal of the same body size. This certainly brings the dietary
requirements back to a more manageable level.
The shortcomings of this outlook are, of course, the same as the
shortcomings of reptiles. Chemical reactions, including biochemical ones,
proceed much more slowly at low temperatures. If the masters of the night
are thus constrained, any of them trying to survive at high altitudes have
a problem. They had best be exceedingly stealthy, for they couldn't outrun
a toddler at 35 degrees Fahrenheit. Given the abundance of vampire legends
from northern countries, this limitation seems unlikely. I do acknowledge
the fondness of Ricean vampires for southerly climates, but they do not
seem to suffer in extreme cold.
Both the mammalian and reptilian models suffer also from the fundamental
assumptions arising from the metabolism of living cells. Neither mammals
nor reptiles function in the absence of oxygen (and I need not be reminded
about hibernating turtles - turtles cheat). Yet a near-universal agreement
seems to hold: the undead need not breathe. We are not discussing
organisms small enough to make simple diffusion a viable option, so I don't
believe that any energetic system which demands oxygen as a terminal
electron acceptor will suffice to explain the phenomenon.
Yet there is, perhaps, a better way. What of a much more fundamental
Energy (in joules) = mass (in kilograms) * 2.997 exp 8 m/sYsquared ..
One gram of material, regardless of water content, yields
8.98x10-to-the-thirteenth joules of energy. This works out to about
2x10-to-the-tenth kcals. Obviously, only a minute fraction of the blood is
used for this purpose, or the problem would be one of disposing of energy
rather than acquiring it. If this suggestion has any validity, most of
the ingested material must be used for structural maintenance and repair of
the body, or excreted in some manner. I am inclined to suggest gaseous
loss, primarily in the form of carbon dioxide, water, and nitrogen.
I will not propose a mechanism for this, as no living animal has yet worked
out a way to pull it off at bio-compatible temperatures. Clearly, though,
this out to be a matter of great interest to the cold-fusion crowd.
- A human-size organism functioning like a mammal needs to feed heavily
and frequently for even minimal survival on blood.
- A human-sized organism functioning like a reptile would get by
energetically, at the cost of putting up with typical reptilian
- Direct conversion of matter to energy (E=mc2) would resolve these
The point of all this is not to pretend that the hunters of the night
cannot exist - blatant folly in view of the number of them reading this -
but to suggest that the biology of magic is a largely unexplored field.
As with more mundane human pathogens, the first major issue in addressing
this problem is the establishment of a model system suitable for
investigation. Thus I have a query for the, shall we say, more senior
readers of this list .. Is your condition transmissible to small rodents,
and if so, what containment procedures are sufficient to manage them?
Vampiric rats might present certain unusual hazards for university animal
The overall problem of approaching vampirism biologically, as this
possibly-myopic entity perceives it, is that of finding an invader capable
of rebuilding its human host to do one of two things. It must either
produce more energy from limited materials than living organisms can manage
by chemical means (the cold fusion suggestion) or it must conserve energy
so dramatically -- without compromising the strength and speed associated
with the condition -- that the scant energy available from blood will
These problems invite speculation that something other than a living
vampiric disease/parasite is involved.
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