A very evident disadvantage under which medical science has labored has
been the impossibility of watching the chemical process set in motion
by substances introduced into the body. For this reason various
experimenters, from time to time, have attempted to "grow tissues"
artificially, in such manner that their development, functions, and
decay--under both healthy and diseased conditions--might be studied
under the microscope. The only way in which this could be done would be
to take a piece of living tissue from the body, and cause its cells to
multiply; tissue being made up of an aggregation of cells.
Science has failed to produce a single living cell, that is, a cell
which will undergo the process of nuclear division (growth) which is
the prime condition of its being; and it seemed equally impossible to
cause a cell already living to undergo the same process if deprived of
the circulation of the blood. Therefore, when in 1910 it was announced
that Dr. Alexis Carrel with his assistant, Dr. M. T. Burrows, had
succeeded, scientific credulity was taxed. A well-known French savant
expressed the opinion before the Society of Biology in Paris, that as
others experimenting along these lines, had witnessed only degeneration
and survival of cells, this phenomenon was all Carrel's discovery
amounted to. In view of past experience, indeed, the chances were in
favor of a mistake. In 1897, Leo Loeb said that he had produced this
artificial growth both within and without the body. Obviously, such
development within the organism where the process of utilizing the
body-fluids, etc., follows the same course as in nature, takes on the
character of grafting rather than of cultivating in a culture medium.
As to causing the external growth, it was ten years later before it
seems first to have succeeded. In 1907 Harrison, from Johns Hopkins
University, furnished details of his research in such form as to be
convincing. But his work had reference to the growth of tissues only of
coldblooded animals, he having cultivated artificially, nerve fibers
from the central nervous system of the frog.
Carrel's work consisted in extending Harrison's method to apply to
warm-blooded animals, including, of course, mammals; he having
primarily in view at this time a more precise knowledge of the laws
governing the restoration of tissues, for example, after serious
surgical wounds. He and his assistant worked steadily to this end, and
succeeded. The tissues of the higher animals, including man, can now be
developed in a culture, and such development can be made to correspond
to a rigidly precise technique. The feat is accomplished by putting
minute pieces of living tissue into a plasmatic (blood) medium which
will coagulate. So complicated is this apparently simple matter in its
application that only the most exquisite surgical skill is proof
against incalculable modifications in results.
Having obtained evidence that tissue can be cultivated in accordance
with a formula that may be relied upon to give definite results, the
effort was made to grow artificially the various malignant (cancerous)
tissues, in turn, of chicken, rat, dog, and human being. Cancerous
tissue invariably developed cancer, and so rapidly and extensively that
the growth could be observed with the naked eye.
It now became evident that, under the right circumstances, the
artificial growth of tissues could be utilized in the study of many
problems; such as malignant growth of tissue; certain problems in
immunity, as, for example, the production of antitoxins of certain
organisms; the regulation of the growth of the organism, or of
different parts of the organism; rejuvenation and senility; and the
character of the internal secretions of the glands, such as the thyroid
which plays a role most important in physical and mental development.
The difficulty lay in the fact that the artificial growth was so very
short-lived. It was found that by passing the growth into a new medium,
and repeating the process, the tissues would begin to grow again; but
their life even under these circumstances was limited at the most to
twenty days. This was manifestly too short a time in which to study the
fundamental questions to which the researchers had addressed
themselves. Thereupon, study was taken up to determine the question as
to _what made these tissues die_. It was found that, apparently as
incidental to growth, there was the process of decay, due to an
_inability of the tissues to eliminate waste products._
On January 17, 1912, experiments were commenced to determine whether
these effects could be overcome. The observations were on the heart and
blood-vessels, artificially grown, of the chicken fetus. These growths
were put into a salt solution for a few minutes at different periods of
their growth, and then placed in a new plasmatic medium. It was found
that by following this method, the tissues could be made to live
indefinitely. When an animal is in the early stages of its development,
the growth of its tissues is necessarily greater as it matures, there
being steady diminution after a certain age until the growth altogether
ceases, and the size of the animal is determined. But it was found by
subjecting these artificial growths to washings in salt solution that
the mass was _fifteen times greater at the end of than at the
commencement of the third month, showing that they do not grow old at
all!_ In the artificial growth the problem of senility and death is
solved.
It was the announcement of this "permanent life of tissues" that caused
such a furor in Paris last summer, and several eminent scientists to
demand ocular demonstration, because "the discovery, if true,
constituted the greatest scientific advance of a generation."
The following summary of this interesting and vitally important and
epoch-making work of Carrel is translated from an article published in
Paris recently by Professor Pozzi, who witnessed the experiments:
"Carrel found that the pulsations of a fragment of heart, which had
diminished in number and intensity _or ceased_, could be revived to the
normal state by a washing and a passage. In a secondary culture, two
fragments of heart, separated by a free space, beat as strongly and
regularly. The larger fragment contracted 92 times a minute and the
smaller 120 times. For three days, the number and intensity of the
pulsations varied slightly. On the fourth day, the pulsations
diminished considerably in intensity. The large fragment beat 40 times
a minute and the little fragment 90 times. The culture was washed and
placed in a new medium. An hour and a half after, the pulsations had
become very strong. The large fragment contracted 120 times a minute
and the small fragment 160 times. At the same time the fragments grew
rapidly. At the end of eight hours they were united and formed a mass
of which all the parts beat synchronically."
Experiments to date seem to establish that the connective tissue, at
any rate, is "immortal."
From this research, it is possible to arrive at certain logical
conclusions, which, however, it remains for the future to confirm. One,
and the most important, is that the normal circulation of the blood
does not succeed in freeing all the waste products of the tissues, and
that this is the cause of senility and death. Were science to find some
way to wash the tissues in the living organism as they have been washed
in these cultures, man's life might be indefinitely prolonged.