Evening star., 1932-05-25
LIFE AND LIGHT
CLOSELY LINKED
Suns Radiation Performs
important Work for All
Organisms.

The threads Of life and light are
interviewer in an intricate pattern.
The minute relationships are shown
in a report of study just issued by the
Division Of Radiation and Organisms
Of the Smithsonian Institution.
The basic factor involved, 1t Is
pointed out by DR.. F. S. Brackett OF the
Smithsonian staff, is the penetration OF
water by different wave lengths OF
radiation. The chief constituent Of all
living things is water. Life arose, posi-
bly, owing in part to the action of radi-
alton from the sun, from the primeval
sea, and remains fundamentally phe-
nomenon of that chemical combination.
Generally speaking, DR.. Bracket ex-
plains, the penetration limit OF any
radiation wave length into a living
organism is predetermined by the trans
mission characteristics of water. Other
substances mixed into the organic COM
plex Of the plant or animal body may
make the penetration much less, but
they hardly can make 1t greater.
Plots Biological Curve.
So the fundamental biological curve,
IN SO far as radiation relationships are
concerned, Is that of water transmission
of light waves. DR.. Bracket has plotted
this relationship from wave lengths OF
approximately 10 microns, ten-thou-
sandth OF a millimeter, which lie far in
the range of the invisible infra-red
band of the spectrum through the bands
of visible and the invisible ultraviolet
light. With this fundamental curve are
compared those of the wave ranges OF
various sources of radiation which are
commonly used - high temperature
lamps familiar in the physicians Office
and the sun. Striking differences are
shown.
For example. the longest visible light
rays which are at the extreme end OF
the red band and measure about Z OF
q micron can go through 80 centimeterS
of water before the light intensity Is
reduced to half its original value. But
q short way farther down the scale In
the infra-red, where the waves are about
q micron and a half in length, the
penetrating power is reduced almost
10000 times The greater part OF the
radiation which comes from the Gus
tomary dull-red therapeutic lamp in the
PHYSICIANS office, it is shown, lies within
this low penetrating infra-red band. It
must be considered a little more than a
surface heater, with little capacity Tor
getting heat into the cells.
Solid Body Is Used.
The next light source considered by
Or. Bracket is solid body at tenn
perature of approximately 5000 de-
grees, such as would be represented by
high-temperature lamp. Such radla-
tion, it is shown, can be expected to
penetrate somewhat into living matter
The greater part of the energy is in the
near infra-red. The greater part OF
the suns energy, on the other hand.
hes in the region of visible light. This
has considerable penetrating power, 1t
Is shown, by the water curve.
A common instrument in medical
practice is the mercury arc lamp. This
produces wave lengths of extreme in
tensity in the violet-blue. yellow
and green bands of the spectrum-but
its most powerful line Of all lies in
the infra-red It is readily transmitted
by both water and flesh. 1t will go
through the aqueous humor OF the eye
ans be absorbed chiefly by the retina,
where it may produce serious burn.
Dr.. Bracket next plots the light pen
Grafton Of flesh. This is greatest Just
between the infre-red and the visible
bands OF the spectrum. The penetra-
ton Of longer waves is cut short by the
tra ansmission capacity Of water. As
the light passes into the visible spec
trum. other constituents Of protoplasm
tend to stop it. It is within the narrow
band between these two-where the
radiation waves range around one mi
cron in length-that there is the great
est possibility of getting heat into the
underlying cells in distinction from
merely heating the surface.
Curious Relationship Band
A curious relationship which NAV
prove Of considerable value In medicine
Is found in the ultra violet band. These
extremely short, invisible waves produce
sunburn They also seem to be asso-
ciated with vitamin D, which prevents
riekets. They produce this necessary
substance in certain food which are
radiated with them. They also seem
to build it up in the body itself
Now, the study shows, the vitamin-
producing wave lengths fall to a large
extent in the very narrow wedge which
lies between the wave lengths most
effective in producing sunburn BY
using this range the possibility is opened
up of raoiating human beings or ami
mails with this vitamin producing radia-
ton much more intensively than has
been possible before without producing
painful burns.
Either the more sunburn- producing
wave lengths could be taken out by
means of filter or by choosing a source
of light whose radiation lies very largely
within the Wtamin creating band, where