Aging Under Glass


As we enter the 20th century, we begin the era of a scientific approach to aging research. Science often proceeds by reducing complex problems into smaller, simpler problems that can be solved one at a time. And so, it was quite logical that someone would take the more complex problem of how animals age and ask the simpler question of whether cells from the body (somatic cells) actually do have an internal clock ticking away that give them only a finite capacity for cell division and tissue regeneration as predicted by August Weismann. The focal point for much of this initial work was to be centered on a new research center in New York City called the Rockefeller Institute for Medical Research founded by John D. Rockefeller Sr. in 1901.

The first director of the Institute was Dr. Simon Flexner. Flexner became known as a tough advocate for a scientific approach to medicine (as opposed to one based on mythology or hearsay). His brother was the author of the widely-discussed “Flexner report”, a critique of medical education at that time, and a call for what is today called “evidence-based medicine.”

One of Simon Flexner’s early hires was a young and ambitious vascular surgeon named Alexis Carrel. Carrel and his colleague Montrose Burrows began research into the cultivation of cells outside the body in laboratory dishes. The concept here is really quite simple. They would take some tissue from the body of an animal (such as those from embryonic chicks taken in a sterile manner before they hatched), then minced up that tissue with sterile scalpels, and put the bits of tissue in a sterile glass dish covered with clotted blood. Carrel and Burrows reported on their results in 19101. One scientific advance reported in this paper was the removal of some of the cells after a few days when they had begun to exhaust the nutrients in the blood into a new glass dish. Today, this process of transferring cells from one dish to another is called the “passaging” of the culture as it allows a subset of cells in one vessel to be moved to a fresh dish where cell division can continue, thereby increasing in cell number over time. In an image reminiscent of a mental image of Al Qaeda in an underground anthrax lab, Carrel and his workers captivated the public imagination.

  Alexis Carrel and his colleagues culturing body cell types in his early 20th century experiments in cell culture.  

Then, in what was perhaps the most sensational of these studies, from 1912-46 Carrel’s group put out a series of publications showing that heart cells taken from an 18 day old embryonic chick, could be moved to fresh dishes repeatedly over the years and that the cells continually divided and proliferated without any signs of the cells aging. This continued life under glass, was despite the fact that they had now greatly exceeded the known lifetime of a normal chicken. The first paper covered the culture of the cells from January 17 to March 19 1912 and was published in a paper called “On the Permanent Life of Tissues Outside of the Organism,” published in the Rockefeller publication The Journal of Experimental Medicine2. In his conclusion he stated:

  “These facts show that experiments made with these or with more perfect techniques and followed over long periods of time may lead to the solution of the problem of permanent life of tissues in vitro, and give important information on the characters acquired by tissues liberated from the control of the organism from which they were derived.”  

Over the subsequent years additional reports followed that were increasingly sensational. In a paper published in 1922, Carrel’s colleague calculated the volume of chick heart cells generated over the years if all kept, would have had a mass greater than the sun3. The media jumped on these stories. A 1921 article by Alessandro Fabbri in The World described a monstrous result being like a “rooster … big enough today to cross the Atlantic in a stride4.” Every anniversary, the lab workers reportedly gathered to sing happy birthday to the famous culture.

Carrel appears to have concluded from these experiments that Weismann’s prediction that body (somatic) cells had an internal clock limiting their replicative lifespan was incorrect, and that when freed from the body, they replicated freely without limit. Therefore, the cause of aging was postulated to be something in the body as a whole, perhaps differences in some unknown substances circulating in the blood, that led to aging. It is rather sad that Carrel published his first paper on the immortal growth of somatic cells outside the body in 1912, two years before the death of Weismann in 1914.

  Alexis Carrel with an attached reporters news wire recounting a lecture of Carrel wherein he predicted mankind’s success in lengthening lifespan.  

Adding to the mystery surrounding Carrel, was his association with the famed aviator Charles Lindberg. On his trip across the Atlantic, Lindberg believed he communicated with some type of transcendent life forms that told him his destiny was to conquer death and transform humans into an immortal species (he admitted this could have simply been hallucinations from lack of sleep). Lindberg formed a collaboration with Carrel, that resulted in the design of a glass heart pump intended to maintain whole tissues in the immortal state outside the body similar to the way the chick cells had been freed from aging. It would appear that their vision was to ultimately rejuvenate human tissues by perfusing them with young blood, thereby keeping the body alive beyond the normal lifespan.

  Alexis Carrel and Charles Lindberg conferring over lunch at the Rockefeller Institute in 1938. Photo in author’s possession.  

The growing public fascination with Carrel beginning with the Nobel Prize for Medicine in 1912, his supposed immortalization of cells, followed by his lectures predicting victory in the battle over aging and death, and his collaboration with the famed Charles Lindberg, led to unprecedented media attention. The mystique this generated was described well by White:

  “…the grey walls, black gowns, masks and hoods; the shining twisted glass and pulsating coloured fluids; the gleaming stainless steel, hidden steam jets, enclosed microscopes and huge witches' cauldrons of the “great” laboratories of “tissue culture5.”  

The Journal of the American Medical Association said of their research: "It is difficult to estimate the importance of this new work. It lays bare practically a whole new field for experimental attack on many of the most fundamental problems in biology and the medical sciences6." This positive appraisal is certainly true in regard to the science of cell culture. However, the results Carrel generated and the conclusions he drew on cell aging and immortalization would not hold up well with history.

Carrel’s Impact on Gerontology Research

Predictably, Carrel’s many publications and the media attention caused the scientific community and the world in general to accept his conclusions. As a result, researchers like C.A. Stephens (discussed elsewhere) looked for environmental or circulating factors that caused cells to age that would, if exposed to a youthful environment to proliferate forever.

Perhaps the most colorful example of how Carrel’s science misdirected medicine was the story of Serge Voronoff. Voronoff made a reasonable analysis of the causes and potential interventions on aging based on the science of his time. Being aware of Weismann’s doctrine of the immortality of the germ-line cells, and yet Carrel’s supposed evidence for the lack of intrinsic aging of the somatic (body) cells, Voronoff laid out a case that the reproductive glands not only contained the immortal germ-line cells, but also were glands that secreted substances into the blood that kept the somatic cells young. As we read in his book How to Restore Youth and Life Longer:


“These glands elaborate the elements of future life which are destined to fecundate the ovule in order to give birth to a new being and to transmit to the species the creative energy held by the individual. At the same time, however, they secrete a liquid which, passing direct into the blood, carries to all the tissues the stimulus and the energy necessary to the individual himself.

In this we are able to observe a marvelous manifestation of the design of creation. In a single organ Nature has united the source of the life of the individual and that of the species7.”


Voronoff therefore concluded that some hormone made by the gonads were the secret of youth. He argued that this hormone could only be effectively administered by transplanting fresh young testicular tissue itself. But where would that tissue come from? He reached for colonies of monkeys. He invented a protocol in which monkey testicles were dissected, and slices of the testicles were transplanted into the testicles of older men to restore virility and reverse the signs of aging.

  Voronoff’s protocol to transfer testicular factors from young monkeys into the body of older men to reverse human aging based on Carrel’s conclusions that somatic cells do not have an intrinsic clock of aging, but instead lose youth through a loss of circulating substances that must be present in the testicles to make babies always born young.  

Voronoff’s protocol became the talk of the town. Evidence of this popularity is seen in it being the subject of a story written by Sir Arthur Conan Doyle called The Adventure of the Creeping Man. In the story, Sherlock Holmes discovers that a mysterious monkey-like creature stalking a young woman is in fact an older man taking Voronoff’s therapy. At the end of the story, Holmes lectures us all that we would be better off without such interventions in the natural order.

Voronoff’s therapy eventually fell out of favor, not so much as due to Holmes’ critique, as to evidence surfacing that Voronoff was giving his patients monkey syphilis. Nevertheless, the administration of estrogen (the female counterpart hormone) was initially trumpeted as a fountain of youth for aging women.

The Hayflick Limit

In about 1959, a young scientist named Leonard Hayflick began a series of experiments at the Wistar Institute in Philadelphia involving the culture of human cells from fetal lung tissue. By this time, the methods of cell culture had advanced significantly over those in use in Carrel’s time. Like Carrel, Hayflick cultured the cells in laboratory dishes and passaged the cells by allowing them to grow until they fill the dish, removing them from the culture dish, then re-plating them at lower densities, to allow them to proliferate again over and over again.

  Dr. Leonard Hayflick while at the Wistar Institute where he first discovered the mortality of human cells cultured outside of the body.  

But Len was disturbed by a troubling fact. After 50-70 doublings, the cells would inevitably slow down and stop. Over time, Len became convinced that this finite doubling lifespan may reflect a natural phenomenon, aging on a cellular level. In 1961 he published a paper titled “The serial cultivation of human diploid cell strains” in the journal Experimental Cell Research where he presented his case that normal human cells had a finite lifespan8. This paper ended up becoming one of the most cited papers in the scientific literature.

What is not as widely known is the fact that Len had earlier submitted his manuscript to the same journal that had previously published Carrel’s results on the immortal growth of chick cells The Journal of Experimental Medicine edited for many years by Simon Flexner and Peyton Rous. As a reflection of the long-lasting legacy of Carrel’s publications, Peyton Rous stated in his letter rejecting Hayflick’s paper:

  “The inference that death of the cells in some of the uninfected cultures is due to “senescence at the cellular level” seems notably rash. The largest fact to have come out from tissue culture in the last fifty years is that cells inherently capable of multiplying will do so indefinitely if supplied with the right milieu in vitro.  

  Letter from an Editor of The Journal of Experimental Medicine rejecting Hayflick’s paper reporting the mortality of human cells isolated from the body based on the legacy of Carrel’s series of papers reporting the opposite result.  

Len has told this writer that in those days he was merely reporting what he was observing in the laboratory, not weighing in on the conflicting views of August Weismann and Carrel. In fact, Len says he was not even familiar at the time with Weismann’s predictions.

Having finally put science back on track, Len’s model of studying aging on a cellular level would simplify research by allowing researchers a reproducible model of human aging in the laboratory. It would remain for future scientists to decipher why human body cells age while reproductive cells continue the species indefinitely as predicted by Weismann in the previous century9.


1. Carrel, A. and Burrows, M.T. 1910. Cultivation of adult tissues and organs outside of the body. J. Amer. Med. Assoc. 55: 1379-1381.

2. Carrel, A. 1912. On the Permanent Life of Tissues outside of the Organism. Journal of Experimental Medicine 15: 516–28.

3. Ebeling, A. H. 1922. A Ten-Year Old Strain of Fibroblasts, J. of Exp. Med. 35: 755–59.

4. Fabbri, A. “Scientists may now Watch Living Connective Tissue Reproduce its Ultimate Cells,” The World, June 12, 1921.

5. White, P.R. 1954. The cultivation of animal and plant cells, New York, Ronald Press, p 6.

6. Editorial 1911. 'Growing tissues outside of the body', J. Amer. Med. Assoc., 56:1722-1723.

7. Voronoff, S. 1928. How to Restore Youth and Live Longer. Falstaff Press, New York. P44.

8. Hayflick L, and Moorhead PS (1961) The serial cultivation of human diploid cell strains. Exp. Cell Res. 25:585-621.

9. West, M.D. 2003. The Immortal Cell. Doubleday (ISBN 0-385-80928-6).



© Copyright 2013 Michael D. West, All Rights Reserved