A Possible Cure for Death, Charles B. Olson, 1988

A Possible Cure for Death, © 1988 by Charles B. Olson
Medical Hypotheses 26 (1988) 77-84 © Longman Group UK Ltd 1988

(This paper is publicly posted here with kind permission of the author, Charles B. Olson.)
[Permalink: http://accelerating.org/articles/apossiblecurefordeath.html]

Abstract

Chemical preservation of the brain may prevent death. Life for an individual human being is inextricably linked to the existence of his or her mind. It is widely accepted that the mind is a product of the functioning of the brain, which, according to this view, is nothing more and nothing less than a fantastically complicated machine. Chemical preservation of the brain (promptly after the cessation of vital functions) preserves not only the neuronal configuration but also a great deal of molecular structure. Thus, it is plausible that a chemopreserved brain contains within it the information of the design of the "brain machine". If so, then technology of the distant future may be able to extract that information and construct a new functionally identical brain machine (as well as a body), thereby allowing the corresponding individual to wake up and live again. It is argued that one's identity is defined by what the brain does rather than how it does it or what it does it with, and therefore that replacement of one's brain with a functionally identical machine does not affect one's identity. Some advantages of chemopreservation relative to cryopreservation as a possible means of preventing death are discussed.

"I wish it were possible, from this instance, to invent a method of embalming drowned persons, in such a manner that they might be recalled to life at any period, however distant; for having very ardent desire to see and observe the state of America a hundred years hence, I should prefer to an ordinary death, being immersed with a few friends in a cask of Madeira, until that time, then to be recalled to life by the solar warmth of my dear country."
- Benjamin Franklin, 1773, in London, after observing the resuscitation (by the warmth of the sun) of two flies which had been found in a bottle of Madeira wine sent from the United States (most certainly they crawled in after opening and 'drowned') (1).

"Is Paul Broca still there in his formalin-filled bottle?"
- Carl Sagan, 1979, reflecting on the preserved a brain of a famous 19th century scientist (2).

Introduction

Human beings are unique among living things in that they alone contemplate their mortality. From the ancient Egyptians preserving their dead in preparation for an afterlife, to Ponce de Leon's futile search for the legendary Fountain of Youth, to modern gerontologists researching the causes and nature of aging, humans have struggled throughout history against death. Indeed, the field of medicine is a product of that struggle. And the success of religions, both ancient and modern, may also be in very large part a reflection of our desire not to die.

Today death is considered to be, at least at present, inevitable. Yet a simple philosophical consideration of the nature of our lives as individual human beings suggests an astounding possibility -- that death may be preventable using technology which has existed for centuries.

Life and death

What is the nature of life for an individual human being? Humans, like all other living things, have been designed by natural selection to reproduce. However, our lives as individuals are not centered around reproduction (at least not for most of us). Many individuals choose not to reproduce, thereby foregoing the possibility of biological immortality offered by having children. As Woody Allen (3) once said,

"Some people want to achieve immortality through their works or their descendants. I prefer to achieve immortality by not dying."

We conceive of immortality as our minds continuing to exist in the future. Life for an individual human being is inextricably linked to the existence of his or her mind. But what is the mind?

An implicit assumption of modern science and medicine is philosophical materialism -- the concept that all facets of existence, including the human mind, are explicable solely in terms of the matter and energy of the physical universe (4-8). Although the. "mind/body problem" is still controversial among academic philosophers (9-11), it is not any longer for most of the scientists who study the brain. As Eric Kandel (12), a prominent neurobiologist, puts it,

"The key philosophical theme of modern neural science is that all behavior is a reflection of brain function. According to this view -- a view that is held by most neurobiologists . . . -- the mind represents a range of functions carried out by the brain. The action of the brain underlies not only relatively simple behavior such as walking or smiling, but also elaborate functions such as feeling, learning, thinking, and writing a poem."

Important evidence linking the brain to the mind comes from studies of accident victims with localized brain damage, dating back to the discovery by the French surgeon Paul Broca in 1861 that human speech is generally produced in the left hemisphere of the brain. Additional evidence comes from experiments (such as those of Wilder Penfield and his colleagues at the Montreal Neurological Institute) in which an electrode is inserted into the brain of a conscious human. Depending upon its location within the brain, passing a current through the electrode can influence consciousness in a remarkable variety of ways, such as producing particular emotions or sensations, or inducing the recall of particular memories (13).

The current understanding of the brain is that it works by means of the electrical activity of the neurons which it contains. A neuron is a cell which is specialized for information processing. It receives signals at thousands of synapses, integrates those signals, and transmits its own resulting signals out along its axon, a long extension of the neuron which terminates with synapses on other neurons. Within the brain, there are billions of neurons and trillions of synapses in a fantastically complex three-dimensional configuration.

The important issue at this point however is not the specific mechanics of how the brain works but rather the premise that the brain is a machine -- a complex mechanism consisting of a large number of atoms and molecules functioning and interacting according to the laws of chemistry and physics.

Another essential consideration is the distinction between one's mind and one's brain. The mind of an individual consists of the functioning of his or her "brain machine". The mind is thus distinct from the brain just as any other process or activity is distinct from the machine which performs it -- just as an instance of computing is distinct from the particular computer which performs. it. If we describe the brain's functioning which produces the mind as "information processing", then the distinction between the mind and the brain is equivalent to the distinction between an instance of information processing and the particular information processor which performs it.

To say that the mind is distinct from the brain does not imply that the mind can exist independent of the machine which produces it; rather it suggests that the "information processing" which is one's mind could be continued with a different machine -- a machine which is functionally identical to one's brain. To extend the above analogies, an instance of computing could be continued with a different (compatible) computer.

The proposition that one's mind could be transferred to a different machine is supported by a basic fact of metabolism: turnover. The great majority of the substance of one's body is gradually replaced with new matter from the food, water, and air that one takes in. [The major exception within the brain is myelin, an inert fatty substance which acts as electrical insulation around axons.] Consequently, the matter which makes up one's brain machine is not constant but rather is constantly changing. Most components (molecules) of one's brain will be replaced many times in the course of one's life. Thus, whereas the information processing continues, the information processor is replaced.

This suggests a novel approach to the prevention of death, one based not on the survival of one's brain in a functional form, but rather on the preservation of the design of one's brain. For one's "brain design" (the information of how one's particular brain works) could be used to create a new functionally identical brain machine. This would allow the information processing (mind, consciousness, etc.) to continue, that is, allow the individual to wake up and live again. This substitution of a new brain machine for the former one can be viewed as a more sudden and complete version of the turnover which occurs naturally.

Brain preservation using chemicals such as formaldehyde, even though it renders the brain permanently nonfunctional, may therefore prevent death by preserving the brain design. A chemically preserved human brain contains an enormous amount of information. Not only is the neuronal configuration preserved, but also a great deal of brain structure at the molecular level (e.g., individual proteins and nucleic acids) is preserved, albeit in a crosslinked or denatured form. Therefore it is plausible that a preserved brain contains the information of the brain design. [The issue of what aspects of brain structure must be preserved is discussed in the next section.]

Death is the permanent cessation of life. It occurs in two distinct stages: first, the cessation of the processes supporting life, and second, the deterioration which makes that cessation irreversible. Thus, although we generally think of death as occurring at the time when one's vital functions cease (e.g., when one's heart stops beating or one's brain electrical activity disappears), it actually occurs sometime later, when the deterioration of the brain has progressed sufficiently to ensure that one's mind will never again exist.

A familiar example of this phenomenon is a heart attack. The heart stops beating and the victim loses consciousness. Although the processes supporting life have ceased, the person is not yet dead since medical intervention may resuscitate him or her within the first few minutes. [After more than a few minutes without blood flow, the brain suffers irreversible damage; however, note that "irreversible" in the context of today's medical technology merely means that the brain will not repair itself given a resumption of blood flow. It does not and cannot refer to any inability of future technology to repair such damage.]

Brain preservation promptly after the cessation of vital functions halts the deterioration of the brain at a very early stage, and allows the possibility of long term storage without further deterioration. In the distant future (e.g., 100 centuries from now), technology may advance to the state where the information of an individual's brain design can be extracted from his or her preserved brain and implemented in a new machine -- the new brain of the individual. The new brain might be organic, as our current brains are, or inorganic, like modern computers. Unlike conventional computers, however, a synthetic inorganic brain would presumably employ a tremendous amount of parallel processing and analog computing, just as our organic brains do.

Of course, the new brain will need to be connected to a fully functional body (organic or inorganic) which will provide the interface to the outside world just as our bodies do today: input from the senses, output to the muscles. A most important benefit of having brains and bodies in which all parts are replaceable is the potential for eternal youth. Furthermore, stored copies of one's brain design would provide a sort of life insurance far more satisfactory than what we have today.

One might fear that a humanmade brain machine would require impractical amounts of space and material; however, let's not forget the example set by nature: such a machine is built in the cramped space within each human skull. One might also object that the development of a humanmade body and brain would be prohibitively expensive. However, one may note that the beginnings of this technology are already being aggressively developed today: artificial limbs, artificial hearts, artificial kidneys and other artificial body parts, and increasingly powerful computer technologies, including parallel processing. When will the development of new technologies cease? Other than the possibility of global thermonuclear war or a catastrophic ecological disaster, it is difficult to visualize it stopping short of what is physically possible. The issue is not whether these amazing technological advances will happen quickly, but rather whether they will happen eventually.

Thus it is proposed that a preserved brain may contain the brain design of the corresponding individual -- a complete description of how that individual's brain produces his or her mind. In the distant future, a new functioning brain and body for that individual could be made, thereby allowing him or her to wake up in that distant future world. In short, brain preservation may prevent death.

Essence: what must be preserved

What aspects of an individual human's brain are essential to his or her brain design? A first point is that only the differences between individuals need be preserved -- aspects of brain structure which are common to all humans will presumably be elucidated by future scientific studies. Most of future knowledge of the human brain will, of course, result from studies of other types of animals such as rodents and nonhuman primates.

A second point is that not all differences are significant. Some aspects of brain structure may be irrelevant to the differences between individuals. For example, membrane lipids are free to diffuse within the two dimensions of the membrane (14), and thus it is implausible that the configuration of lipids within the membrane encodes any information essential to an individual's brain design.

A third point which also reduces the scope of what must be preserved is that there is a great deal of redundancy of information within the brain. Many pieces of information about particular aspects of brain structure and function are incorporated independently in more than one location within the brain. An obvious example is the genome, which is stored independently in each cell nucleus within the brain.

A second example of redundancy involves the locations of the neuronal membranes (i.e. the neuronal configuration). The information of the membranes' positions is contained not only in the physical positions of the membrane lipids, but also in the cellular cytoskeleton (which is made of proteins) whose purpose is, among other things, to hold the membrane in its configuration (15). Thus, even if a substantial proportion of lipids were extracted in the course of chemical preservation of a brain (as is the case with some preservation techniques), it is plausible that the information of the neuronal configuration would still exist in the crosslinked cytoskeletons of the neurons.

The vastly complex three-dimensional configuration of neurons, including their axons, dendrites and synapses, is the most obvious candidate for a structure which reflects the differences between the minds of individuals. While humans in general have large-scale brain anatomy in common (hippocampus, hypothalamus, Broca's area, etc.), each individual has his or her own unique neuronal configuration (within these structures) which is believed to account for a large part of the differences between individuals. To quote Eric Kandel (16) once again,

"Many neurobiologists believe that the unique character of individual human beings, their disposition to feel, think, learn and remember, will ultimately be shown to reside in the precise patterns of synaptic interconnections between the neurons of the brain."

However, other aspects of the brain may also be essential. For example, the positions and types of the ion channels (voltage- and/or chemical-sensitive transmembrane ion gates made of proteins) in the neuronal membranes may be important contributors to the functional differences between the brains of individuals. [Note that, similarly to the above example, ion channels may be held in place not only by the membrane but also by the cytoskeleton (15).]

The neuronal configuration together with the positions and types of ion channels within it may plausibly contain sufficient information to specify the brain design of the corresponding individual. Which other aspects (if any) of the brain need also be preserved won't be known until the functioning of the brain is far better understood.

Nonetheless there is, in any case, persuasive evidence that the physical structures specifying the individual's brain design are not labile (easily destroyed), thereby giving reasonable hope that they can be permanently preserved. First, learning and memory storage require protein synthesis in order to become permanent (17). In other words, long-term changes to the mind do not take place instantaneously but rather require significant anabolic (constructive) activity. Second, the mind can survive conditions which can eliminate most, if not all, electrical activity in the brain (cooling, anesthesia, disruption of the blood supply, etc.). Therefore, reverberating cortical circuits or other ephemeral aspects of brain function cannot be responsible for longterm aspects of the mind since the above treatments do not permanently alter one's mind. These facts support the contention that chemical brain preservation may preserve an individual's brain design.

Identity: will it be you?

But will the mind produced by the functioning of your reconstructed brain really be "you"? Specifically, let us ask whether any of the three following alterations would change your identity:

1. Changes in the substance of the brain which do not affect the design of the brain;
2. Changes in the design and substance of the brain which do not affect the process performed by the brain;
3. Small errors in the reconstruction of the brain.

1. Changes in substance: In effect, the experiment of substitution has already been performed in each of us. We can be confident that changes in the particular substance of the brain do not affect one's identity because, as mentioned above, the great majority of the substance of the human brain turns over in the course of normal metabolism.

2. Changes in design and substance: Although the basic idea of this article is that one's brain design must be preserved to prevent death, the design is only a means to an end. The ultimate goal is not to construct a machine with an identical design per se (although that would of course accomplish the goal), but rather to construct a machine, any machine, that will perform the same process (i.e., produce the mind).

From our experience with humanmade machines, we know that it is often possible to perform a process with machines of widely varying design. A motor may work by means of electromagnetism, internal combustion, thermonuclear fusion, or many other combinations of matter and form, but what the motor does (the production of mechanical power) remains unchanged. Less trivial examples are a digital computer functioning by means of mechanical gears (instead of transistors), and an analog computer consisting of water flowing through pipes and reservoirs (instead of electrons flowing through resistors and capacitors).

A similar design (and substance) substitution may also be possible for the human brain. In the distant future, scientists may be able to construct a new brain machine for an individual which would have a different design (and substance) than the original organic brain but which would perform the same process. For example, it is conceivable that a machine using flows of electrons through inorganic materials could do what an organic brain does using flows of ions around and across neuronal membranes. This is not to argue that this sort of a design (and substance) substitution must be possible, but rather that if it can be done then one's identity will not be changed. For one's identity is defined by the mind rather than the brain -- by what the brain does rather than how it does it (its design) or what it does it with (its substance).

3. A margin for error: Is there a margin for error? Would any error in the reconstruction of the brain machine, no matter how small, result in a change in the individual's identity?

In the course of our lives, there are many events which change (and usually damage) our brains and, consequently, our brain designs and our minds: strokes, drug abuse, accidents, diseases such as Alzheimer's, etc. All of these types of damage can range in significance from the trivial to the lethal. Do all instances of damage, no matter how insignificant, change the identity of the individual? Does a trivial change make someone a "different person"?

No. When dealing with damage or other changes to individuals, we allow a margin for error. These familiar changes to our brains and minds are and must be evaluated according to their significance to brain function. Therefore, if brain preservation and reanimation can be achieved with a change which is less than (for example) that of a mild concussion, then just as the concussion does not alter one's identity, neither would such a preservation/reanimation procedure. Thus there is a margin for error applicable to the reconstruction of the brain machine of an individual.

Chemopreservation and cryopreservation

Technology for the chemical preservation of the fine internal structure of the brain has existed for centuries. An essential technique is perfusion, the process of introducing a solution into a tissue by means of the vascular system. Perfusion enables chemical preservatives, such as formaldehyde or glutaraldehyde, to be introduced into the brain in a rapid and uniform fashion. Rapidity is essential because the degradative enzymes in the cells of the brain must be quickly inactivated; otherwise they would soon destroy the brain's internal structure. Uniformity is important because it enables preservatives to be introduced at an optimal concentration throughout the brain.

The key discovery which led to the development of perfusion was the elucidation of the circulation of the blood by the English physician William Harvey in 1628 [although Leonardo da Vinci (1452-1519), the great Italian sculptor, painter, and scientist, is believed to have preserved specimens for dissection by venous injection]. Arterial embalming developed soon thereafter, largely as a method of providing satisfactory material for dissection.

A famous case of arterial embalming was performed in 1775 on the wife of a Dr. Martin Van Butchell -- her marriage settlement specified that her husband could control her fortune "as long as she remained above ground." The preserved lady, dressed in a fine linen gown, became a tourist attraction, and was eventually moved to the museum of the Royal College of Surgeons [she was destroyed by the German bombing of London in 1941] (18). However, not until the late 19th century did arterial embalming become widely used in conjunction with funerals (19).

Also important was the development of the microscope by the Dutch naturalist Antonie van Leeuwenhoek around 1670. Subsequently scientists devised a wide variety of processes for preserving the internal structures of tissues so that they could be observed under a microscope (20, 21). Since a tissue must be rigid in order to be cut into thin slices, the technique of embedding a specimen within a solid substance such as wax (with the wax permeating throughout the tissue sample) was developed. In the past few decades, as a result of the advent of electron microscopy, new embedding materials, especially plastics, have been developed which are highly resistant to the damage of an electron beam and which aim to minimize the problem of spatial distortion within the specimen (22).

The technological advances in the preparation of tissue for microscopy have directly improved the prospects of brain preservation for reanimation. This is not a coincidence: the goals of microscopy and brain preservation for reanimation are fundamentally similar. In both cases, a maximal amount of structural detail is preserved such that information can be extracted.

In addition to chemopreservation, there is a second method of preserving the internal structure of the brain: cryopreservation (low temperature preservation). The modern era of research into cryosuspension (suspended animation via low temperatures) began with the discovery by Polge, Smith, and Parkes in 1949 that bird spermatozoa could survive being frozen in a glycerol solution (23). Researchers were initially confident that cryosuspension of large complex organisms such as mammals would soon be achieved. However, although progress has been made (for example, some normal healthy children alive today once existed as frozen human embryos (24)), it is not yet possible to freeze and revive large organisms (25).

Despite the limitations of the technology, Robert Ettinger, in his 1964 book The Prospect of Immortality (26), proposed human cryopreservation as a means of possibly preventing death. Ettinger's basic idea is that eventually technology may be able to repair both the freezing damage and the damage which caused the "death" of the person. Although a small following has resulted (a few dozen individuals have been frozen to date, and a few hundred have made arrangements to do so) (27), the scientific community has by and large rejected the possibility of life after cryopreservation as currently performed because of the widespread damage caused to the cells by the freezing process (1, 28).

But is repair necessary at all? If the information of the brain design is preserved and extractable, then replacement (rather than repair) of the brain is a valid alternative. Thus, cryopreservation should be reevaluated. The criterion for evaluating its success should not be the retention of viability of the cells of the brain -- they can all be lethally damaged, as they are in chemopreservation; rather, success should be measured in terms of the preservation in an extractable form of the structural information which is believed to be relevant to the individual's brain design.

Both cryopreservation and chernopreservation do damage to the internal structure of the brain. However, both preserve the neuronal configuration, and both retain a great deal of additional information in terms of the location and identity of molecules within the brain. Furthermore, because in each case the damage is produced in a systematic manner, it may be possible, to some extent, to infer structures which existed before the damage.

Regarding the extraction of the information of the brain design, chernopreservation has a marked advantage relative to cryopreservation. The molecules in a chemopreserved brain have been extensively crosslinked and can be embedded in a plastic which was designed for electron microscopy. Consequently they will be resistant to the heat and damage generated by whatever beam of particles (or other investigative device) is used to determine the details of the internal structure. In contrast, a frozen brain is not particularly prepared to resist damage, and is acutely sensitive to any heat generated. This problem of information extraction applies to any proposed repair of the cryopreserved brain as well -- repairs can be made only after the relevant details of the structure are known. Of course, these technical problems may eventually be overcome; one should hesitate before placing limits upon the technology of the limitless future.

Chemopreservation has some additional advantages relative to cryopreservation. First of all, it is far less expensive: whereas cryopreservation requires long-term liquid nitrogen storage, chemopreservation is a one-time expense. A chernopreserved brain, embedded in a block of plastic, is inherently resistant to damage, and it can be easily stored nearly anywhere with additional forms of protection if desired. In contrast, a cryopreserved brain is at risk of thawing, and any additional protection must be done in conjunction with the liquid nitrogen storage. Finally, a form of chernopreservation of the brains of the recently deceased (i.e., funereal embalming) is already highly developed and widely practiced today, albeit for quite a References different purpose (19). Indeed, the cost of brain chernopreservation could be less than that of a typical funeral. For these reasons, chemopreservation may succeed in the marketplace where cryopreservation has thus far had only limited success.

Conclusion

Thus, a preserved brain may in fact be an individual in a state of suspended animation, not in a biological sense but rather in the sense related to consciousness and the mind. Just as anesthesia temporarily halts our lives as conscious individuals, so may brain preservation allow a lengthy but ultimately temporary halt in conscious life, like a long, deep and dreamless sleep.

From the narrow perspective of our everyday lives, a day 100 centuries hence may seem remote to the point of absurdity. Yet our present day will eventually take its permanent place in the ancient history of humankind. That distant future day will come. And it could be the first day of the rest of your life.

Death is destruction. It is the passage of existence into permanent nonexistence. It is natural to fight it.

The ancient Egyptians fought death with chemical preservatives (29). They believed that the soul would not permanently leave the body as long as the body remained intact. Unfortunately, they also believed that the heart, and not the brain, was the seat of intelligence. Consequently, whereas the heart of the dead person was carefully preserved, the brain was scooped out and discarded like so much oatmeal. It is ironic that a modern version of their preservative art may well allow us to succeed where they failed.

Acknowledgement

I would like to thank Lisa Butler for her invaluable assistance in editing the manuscript.

Addendum

Since writing this paper, I have found that my major thesis -- that chemical preservation of the brain may prevent the death of an individual human being -- has also been proposed by K. Eric Drexler in Engines of Creation, Anchor Press/Doubleday, Garden City, NY, 1986; see pages 111-113, 133-138, 267.

References

Prehoda R. Suspended Animation. Chilton Book Company, Philadelphia, 1969. [The quotation by Benjamin Franklin is on page 5. It is taken from a letter to Jacques Barbeu Dubourg, dated April, 1773.
Sagan C. Broca's Brain. Random House, New York, 1979. [The quotation is on page 9.]
Mann J A. Secrets of Life Extension. Harbor Publishing, San Francisco, 1980. [The quotation by Woody Allen is on page 12.]
La Mettrie J 0. L'Homme Machine (Man a Machine). (G C Bussey, M W Calkins, Translators). Open Court, La Salle, IL, 1961. [The original work was published in 1748.]
Huxley T H. On the Hypothesis that Animals are Automata, and its History. p. 199 in Collected Essays of T. H. Huxley, Vol. 1. D. Appleton and Co., New York, 1874.
Jeannerod M. The Brain Machine: The Development of Neurophysiological Thought. (D Urion, Translator). Harvard University Press, Cambridge, MA, 1985. [The original work was published in 1983.]
Doty R W. Philosophy and the Brain. Perspectives in Biology and Medicine 9: 23, 1965.
Broad W J. Lost in Thought. Science News 114: 360, 1978. [This is a brief history of the understanding of the brain and intelligence]
Schaffer J. The Mind-Body Problem. p. 336 in The Encyclopedia of Philosophy, Vol 5 (P Edwards, ed) Macmillan, New York: 1967.
Morick H. (ed) Introduction to the Philosophy of Mind: Readings from Descartes to Strawson. Scott, Foresman & Co., Glenview, I L, 1970.
Haugeland J. (ed) Mind Design: Philosophy, Psychology, and Artificial Intelligence. Bradford Books, Montgomery, VT, 1981.
Kandel E R. Brain and Behavior. p. 3 in Principles of Neural Science. 2nd ed. (E R Kandel, J H Schwartz, eds) Elsevier, New York, 1985. [The (first) quotation by Eric Kandel is on page 3.]
Sheer D E. (ed) Electrical Stimulation of the Brain. University of Texas Press, Austin, Texas, 1961. [pp. 533-553 is a review of Wilder Penfield's work.]
Stubbs C D. Membrane Fluidity: Structure and Dynamics of Membrane Lipids. Essays in Biochemistry 19: 1, 1983.
Darnell J, Lodish H, Baltimore D. Molecular Cell Biology. Scientific American Books, New York, 1986. [See page 592.]
Kandel E R. Small Systems of Neurons. Scientific American 241: 66, 1979. [The (second) quotation by Eric Kandel is on page 67.]
Gibbs M E, Mark R F. Inhibition of Memory Formation. Plenum, New York: 1973. [pp. 57-75 deals with amnesia caused by protein synthesis inhibitors.]
Mitford J. The American Way of Death. Simon and Schuster, New York, 1963.
Strub C G, Frederick L G. The Principles and Practice of Embalming. 4th ed. L G Frederick, Dallas, Texas, 1967. [pp. 13-48 is a history of funeral practices and embalming.]
Bancroft J D, Stevens A. (eds) Theory and Practice of Histological Techniques. Churchill Livingstone, Edinburgh, 1977.
Culling C F A, Allison R T, Barr W T. Cellular Pathology Technique. 4th ed. Butterworths, London, 1985.
Hayat M A. Principles and Techniques of Electron Microscopy. Vol. 1. 2nd ed. University Park Press, Baltimore, 1981.
Polge C, Smith A, Parkes A S. Revival of Spermatozoa after Vitrification and Dehydration at Low Temperatures. Nature 164: 666, 1949.
Trounson A. Preservation of Human Eggs and Embryos. Fertility and Sterility 46: 1, 1986.
Jacobsen I A, Pegg D E. Cryopreservation of Organs: A Review. Cryobiology 21: 377, 1984.
Ettinger R C W. The Prospect of Immortality. Doubleday, Garden City, NY, 1964.
Smith G P. Medical-Legal Aspects of Cryonics: Prospects for Immortality. National University Publications, Associated Faculty Press, Port Washington, NY, 1983.
Comfort A. Imitations of Immortality. Medical Opinion 7: 310, 1971.
Hamilton-Paterson J, Andrews C. Mummies: Death and Life in Ancient Egypt. Penguin Books, New York, 1979.

Thanks for visiting