Table Of ContentAMERICAN INSTITUTE OF BIOLOGICAL SCIENCES
and
U. S. ATOMIC ENERGY COMMISSION
MONOGRAPH SERIES ON
RADIATION BIOLOGY
JOHN R. OLIVE, Series Director
AMERICAN INSTITUTE OF BIOLOGICAL SCIENCES
ADVISORY COMMITTEE
AUSTIN M. BRUES, Argonne National Laboratory
LEO K. BUSTAD, Pacific Northwest Laboratory
ERNEST C. POLLARD, Pennsylvania State University
CHARLES W. SHILLING, Biological Science Cornmunications Project
MONOGRAPH TITLES AND AUTHORS
RADIATION, RADIOACTIVITY, AND INSECTS
R. D. O'BRIEN, Cornell University
L. S. WOLFE, Montreal Neurological Institute
RADIATION, ISOTOPES, AND BONE
F. C. MCLEAN, University of Chicago
A. M. BUDY, University of Chicago
RADIATION AND IMMUNE MECHANISMS
W. H. TALIAFERRO, Argonne National Laboratory
L. G. TALIAFERRO, Argonne National Laboratory
B. N. JAROSLOW, Argonne National Laboratory
LIGHT: PHYSICAL AND BIOLOGICAL ACTION
H. H. SELIGER, Johns Hopkins University
W. D. MCELROY, Johns Hopkins University
MAMMALIAN RADIATION LETHALITY: A DISTURBANCE IN CELLULAR
KINETICS
V. P. BOND, Brookhaven National Laboratory
T. M. FLIEDNER, Brookhaven National Laboratory
J. O. ARCHAMBEAU, Brookhaven National Laboratory
IONIZING RADIATION: NEURAL FUNCTION AND BEHAVIOR
D. J. KIMELDORF, U. S. Naval Radiological Defense Laboratory
E. L. HUNT, U. S. Naval Radiological Defense Laboratory
TISSUE GRAFTING AND RADIATION
H. S. MICKLEM, Radiobiological Research Unit, Harwell
J. F. LOUTIT, Radiobiological Research Unit, Harwell
(IN PREPARATION)
TRITIUM IN BIOLOGY
L. E. FEINENDEGEN, Services de Biologie, Euratom
PHYSICAL ASPECTS OF RADIOISOTOPES IN THE HUMAN BODY
F. W. SPIERS, University of Leeds
THE SOIL-PLANT SYSTEM IN RELATION TO INORGANIC NUTRITION
M. FRIED, International Atomic Energy Agency, Vienna
H. BROESHART, International Atomic Energy Agency, Vienna
MUTAGENESIS
I. I. OSTER, Institute for Cancer Research, Phihdelphia
LIGHT:
Physical and Biological Action
HOWARD H. SELIGER
WILLIAM D. MCELROY
McCollum-Pratt Institute
and
Department of Biology
The Johns Hopkins University
Baltimore, Maryland
Prepared under the direction of the American Insti-
tute of Biological Sciences for the Division of Technical
Information, United States Atomic Energy Commission
1965
ACADEMIC PRESS · New York and London
CoPYRGiHT © 1965 BY ACADEMIC PRESS INC.
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First Printing, 1965
Second Printing, 1966
PRINTED IN THE UNITED STATES OF AMERICA
FOREWORD
This monograph is one in a series developed through the cooperative
efforts of the American Institute of Biological Sciences and the U. S.
Atomic Energy Commission's Division of Technical Information. The
goal in this undertaking has been to direct attention to biologists' increas-
ing utilization of radiation and radioisotopes. Their importance as tools
for studying living systems cannot be overestimated. Indeed, their appli-
cations by biologists has an added significance, representing as it does the
new, closer association between the physical and biological sciences.
The association places stringent demands on both disciplines: Each
must seek to understand the methods, systems, and philosophies of the
other science if radiation biology is to fulfill its promise of great contribu-
tions to our knowledge of both the normal and the abnormal organism.
Hopefully, the information contained in each publication will guide
students and scientists to areas where further research is indicated.
The American Institute of Biological Sciences is most pleased to have
had a part in developing this Monograph Series.
JOHN R. OLIVE
Executive Director
American Institute of Biological Sciences
v
PREFACE
Research in the field of photobiology is extremely diverse and requires
a concurrent knowledge of the physics of electromagnetic radiation,
molecular structures, and the biology of the organisms. Any effort, there-
fore, to summarize such areas as the measurement of molecular excitation
by light, photosensitization, photosynthesis, phototropism, phototaxis,
vision, photoperiodism, bioluminescence, diurnal rhythms, and effects of
ultraviolet and X-ray on cells, tissues, and organisms in one volume is
obviously difficult inasmuch as each subject could fill an entire volume.
We have been encouraged to do this, however, even with these limitations
in mind, in order to give beginning students a general introduction to the
important problems which are usually considered in photobiology. It is
evident, because of the large amount of detailed information available,
that the student would have considerable difficulty in trying to obtain an
over-all view of the broad field of photobiology using current reviews and
advanced monographs. This is particularly true in the physical aspects.
Because of the nature of the subject, therefore, it has been necessary to
condense, or even omit, many significant investigations, and for this we
apologize to our colleagues in the field. In addition, because of the nature
of the backgrounds of the authors, it is to be expected that some subjects
have been covered more fully than others. In trying to condense and sum-
marize, however, we hope that where other viewpoints could have been
presented but were not, we have made this clear in the text and referred
the student to other publications.
In addition to the purely biological aspects, there is a great need for a
general introduction to physical concepts and their practical application
that is not adequately covered in general and intermediate physics
and chemistry courses. We have tried to summarize this material in the
first two chapters. We hope that we have left the reader with at least one
important concept, that all problems of photobiology or all processes
which are initiated by light are quantum phenomena and should always
be considered as such even though there may be enzymatic amplification
after the initial photochemical events.
We have had numerous discussions with many colleagues in the field,
some of whom have read certain parts of the manuscript. We would like
to thank Dr. M. Kasha and Dr. S. Udenfriend for their comments, Miss
Marie Pierrel who drew many of the illustrations in the monograph, and
vu
viii PREFACE
Mrs. Mary E. Backer who very patiently typed her way through masses
of very roughly written drafts.
We would like to take this opportunity to express oar deepest appreci-
ation to two very understanding women, to whom this book is sincerely
dedicated.
HOWARD H. SELIGER
WILLIAM D. MCELROY
March, 1965
CHAPTER 1
Measurement and
Characterization of Light
1. The Nature of Light
The whole of nature is a trillion, trillion chemical machines, squirming,
twisting, swimming, crawling, floating, flying, and sometimes walking—in
the image of Man.
What a spectacle is this vast proliferation of green light-traps, utilizing
in a special still-secret process the energy of sunlight to convert carbon
dioxide, water, and inorganic salts into more complex molecules at the
rate of 375 billion tons of carbohydrates per year. And picture still further
the voracious horde of plant-eating animals and animal-eating animals
that somewhere in the dim past have given up this basic light-energy
conversion process and are utterly dependent upon these green alchemists
and, ultimately, upon the light from the sun. For aside from the minor
heating of the earth's crust by the naturally radioactive elements, volcanic
eruptions, cosmic rays, and fusion reactions, all of the energy for life on
earth is contained within a narrow spectral range of electromagnetic
radiation received from the sun. The total solar radiation (cal/cm 2-min)
at normal incidence outside the atmosphere at the mean solar distance
is 2.00 ±2% (Smithsonian Physical Tables, 1959, Table 808). This cor-
responds to a total incident energy of 1.34 X 1024 cal per year or an
irradiance of 0.14 watts/cm2. In the equivalent units of mass and energy
this is a total of 68,400 tons of sunlight falling on the earth per year.
Table 1.1 gives a summary of the distributions of this incident sunlight in
the different wavelength regions of the spectrum.
A large variety of physical phenomena are defined either subjectively
or physiologically and in most cases with very good reasons. The definition
of light is intimately associated with its physiological response. The
smallest child knows that "light is to see." This simple definition tells
him much more than "light is radiant energy in that portion of the
transverse electromagnetic spectrum with frequencies between 3.8 X 1014
and 7.7 X 1014 cycles per second or with vacuum wavelengths between
7800 and 3900 A, respectively, capable of stimulating, in the normal
1
2 LIGHT: PHYSICAL AND BIOLOGICAL ACTION
human eye, the sensation of vision." In fact the former definition by
virtue of its brevity is less subject to contradiction than the latter. For
example, the early workers in radioactivity were able to observe a dull
glow upon holding a strong source of radium near their eyes in a dark
room; likewise the early X-ray workers, upon exposure to an X-ray
beam—a type of scientific "derring-do" that makes one shudder at their
intrepidity or naivité. It is also a well-known fact that persons who have
suffered from cataracts, who have therefore had their lenses removed,
are able to "see" in ultraviolet light below 3800 A; the normal lens
apparently absorbs all wavelengths below this value. Honeybees have a
component of color vision in the ultraviolet. Many color-blind persons,
TABLE 1.1
SPECTRAL DISTRIBUTION OF SUNLIGHT INCIDENT ON EARTH'S ATMOSPHERE
Einsteins per sec-
Wavelength Per cent of Mwatts/cm2 ond over total
region (A) incident energy (X 103) surface« (X 109)
Below 2000 0.1 0.136 0.255
2000-2500 0.8 1.09 2.63
2500-3000 2.2 2.99 8.77
3000-3500 3.5 4.76 16.5
3500-4000 5.4 7.34 29.5
4000-7000 36.0 49.0 288
7000-10,000 24.0 32.6 295
Above 10,000 28.0 38.1
a 1 Einstein = 6.025 X 1023 light quanta.
although they cannot distinguish red light, have dark-adapted vision
which is just as acute as that of persons with normal eyes. A sharp blow
on the head, the action of certain drugs, or mental aberrations can produce
the sensation of brilliant colors.
With these facts in mind let us now proceed to discuss light from a
purely physical and historical viewpoint, and then perhaps it will be
easier to relate these physical concepts to biological applications.
Let us begin our story with Sir Isaac Newton, born in Woolsthrope,
England, in 1642, only 11 years after the ''heretic" Galileo had for the
second time been called before the Inquisition because of his vocal opposi-
tion to the Ptolemaic, earth-centered solar system. In addition to Newton's
magnificent contributions of the Differential Calculus to Mathematics
and the Universal Law of Gravitation to Mechanics, he discovered in
1666 that white light is made up of the various spectral colors which
could be "sorted-out" by means of a prism and which he explained on the
1. MEASUREMENT AND CHARACTERIZATION OF LIGHT 3
basis of light corpuscles (''multitudes of unimaginable small and swift
corpuscles of various sizes springing from shining bodies . . . ").
His fame and stature as a monarch of science overshadowed the work
of another genius of that era, Christian Huygens, who in 1678 had devel-
oped a wave theory of light. It was not until 1801 when Thomas Young,
in a paper before the Royal Society, presented an undulatory theory of
light and proposed the phenomenon of interference to explain refraction
and the diffraction grating, that the wave theory again dared to lift its
head. Even at this late date Young was subjected to a storm of derision
and abuse by some of his more dogmatic scientific peers. It was only after
the crucial experiments of Jean Leon Foucault in 1850, who showed that
light travels more slowly in a dense medium such as water than in a rare
medium such as air, as predicted by the wave theory, that the wave
theory became respectable.
Paralleling these developments in experiments with light were the
discoveries in electricity and magnetism. In 1820 Hans Christian Oersted
showed that there is a magnetic field associated with the flow of electric
current. In 1831 the self-taught experimental genius Michael Faraday
discovered the converse—that there is an electric current associated with
a change of magnetic field, the principle of the dynamo. Then in 1865,
James Clerk Maxwell, Professor at King's College, London, published his
"Dynamical Theory of the Electromagnetic Field," which clearly ranks
with Newton's "Principia" as one of the tremendous landmarks in science.
In this treatise Maxwell combined the discoveries of Newton, Huygens,
Young, Foucault, Oersted, and Faraday into a unified theory of electro-
magnetic phenomena which included light. Light consisted of transverse
electromagnetic waves (an assumption made by Auguste Jean Fresnel
in 1818 to explain polarization) whose frequency of vibration v and wave-
length λ were related by v\ = v, where v is the speed of propagation of
light in the medium. In vacuum in the Maxwell theory v = c, a uni-
versal constant, dependent only upon the ratio of the electromagnetic
to the electrostatic unit of charge. The value of this ratio even at that
time agreed to better than 1 % with the experimental value for the speed
of light, measured in 1849 by Hippolyie Louis Fizeau, and represents
one of the great triumphs of theoretical physics.
One of the corollaries of Maxwell's theory was that light was pictured
as a series of rapid alterations of electric and magnetic fields, each per-
pendicular to the other and both transverse to the direction of propagation.
In 1887 Heinrich Hertz, in Germany, showed that an electric dis-
charge or an oscillating electric dipole radiated energy in the form of
transverse waves which traveled with the speed of light and possessed all
of the wave properties predicted by Maxwell's electromagnetic theory. It
4 LIGHT: PHYSICAL AND BIOLOGICAL ACTION
is interesting to note that during the course of these experiments he
accidentally discovered the Photoelectric Effect, one of the fundamental
phenomena which require the quantum (corpuscular) theory and which
cannot be explained by the very electromagnetic wave theory whose
existence he was at the same time demonstrating.
Maxwell's theory gave a mechanism of an oscillating charge giving
rise to electromagnetic waves and from L. Lorenz1 mathematical picture
in 1880 of a quasi-statically bound charged particle, the idea was devel-
oped that very rapid oscillations of charged particles can give rise to elec-
tromagnetic waves of very high frequency, i.e., light.
In 1897, Joseph John Thompson showed that cathode rays consisted
of particles of negative charge, or electrons. In the same year the Normal
Zeeman Effect of a magnetic field on the emission of light was discovered
by Pieter Zeeman and interpreted by Hendrik Antoon Lorentz and Zeeman
on the basis of an electron linear oscillator as a model for the radiating
atom. The wave theory appeared firmly established. But there were
rumblings. Some of the experimental facts would not fall neatly into
place. First, there was Hertz' photoelectric effect, the emission of electrons
by a material irradiated by light, which had a threshold wavelength
above which it did not occur no matter how much energy was absorbed,
a result at variance with the wave theory. Then, there were other more
complicated theoretical problems. Last, based on thermodynamics and
the Law of Equipartition of Energy, the wave theory predicted that the
radiant energy emitted from a blackbody should increase rapidly to
infinity as the wavelength approaches zero, referred to as the * infinity
catastrophe." Since experimentally the spectral energy distribution was
found to be a peaked curve with a maximum predicted by the Wien
Displacement Law and the total energy emitted was finite and followed
the Stefan-Boltzmann Law, it was evident that there was something
incorrect in the expanding wave-front picture of the wave theory which
could not account for either the absorption of all of the energy in the
wave front by a single oscillator or the spectral distribution of energies
from a group of oscillators. In 1901 Max Planck, in one of the most
startling breaks with the whole of scientific tradition, reluctantly put
forward the hypothesis that radiation is discontinuous. If, in the expres-
sion for the average energy of an oscillator, the assumption was made that
an oscillator could not emit all possible energies but could emit one of the
discrete values, hvu where h was a universal constant and Vi was the fre-
quency of the light, the predicted energy distribution from a blackbody
was in exact agreement with experiment. The "infinity catastrophe" was
removed and the Wien Displacement Law and the Stefan-Boltzmann Law,
both based on pure thermodynamic reasoning, were unchanged. Although
