Evening star., 1928-11-04
VISION IS CHEMICAL,
PROFESSOR HOLDS.
Theory Applies to Animals as
Well as Humans, Says
DR.. HeCht.

Al
physical processes of vision. which ap-
parently act In the same way through
out the animal kingdom and may even
extend to plants, was expounded last
night by DR.. Selig Hecht of Columbia
University at a joint meeting of the
American optical Society and the Bio
logical Society of Washington at the
Cosmos Club.
When light falls on the eye, DR. Hecht
said, 1t strikes a known chemical sub
stance. visual purple, which has been
isolated from the rods of the eye and
subjected to extensive tests. The light
apparently has chemical effect on
this purple, splitting it into two SUBJ
stances now known as P and A. These
have not been isolated.
Process of Vision.
At low intensities of light only minute
amounts OF these two substances are
created and they recombine Immediately
into visual purple. In these cases the
light stimulus is below the threshold of
vision and there Is no consciousness Of
it,
At higher intensities the two sub
stances are created in such amounts
that they do not recombine as fast as
they are made, but either one or the
other OF them combines with second
substance In the eye which has not been
localized and Is now purely hypothetical.
This second combination sets up an i'm
pulse, possibly electrical, along the visual
nerve fibers to the brain and the result
Is vision.
DR., Hecht told of a long series of
experiments with lower animals, notably
clans, which showed in every respect
the same visual mechanism as the
higher animals and humans.
Tests Made on CLANS. ,
He found In clans the same sensitiv-
ity to very weak light that is shown by
human eyes when light Is turned on
in a dark room, although daylight,
which does not have such a powerful
stimulating effect once the eye has been
adjusted to it, is 10000 times more in
tense. This he explained by the as
sumption that the visual purple be-
comes reconcentrated in the dark.
Throughout the animal kingdom, he
said, light Is not seen until some time
after 1t Is turned on, and continues to
be seen for some time after it is turned
oh-the principle upon which both the
motion picture and television is based.
Also minimum threshold intensity is
required in all creatures before there is
sensttivity to light.
Carbon Reduces Pressure.
Big doses of carbon arc or irradiation
OF the body tend to lower blood pres
sure and may become recognized
treatment for some high-blood pressure
conditions, DR.. Henry Laurens of
Tulane University told the American
Optical Society meeting at the Bureau
OF Standards yesterday. Decreases of
from 8 to 10 per cent for several months
have been reported, he said, with a cor
responding increase in the pulse beat,
which may result from rest rather than
light treatment. The blood pressure of
a dog subjected to light doses of from
IS to 125 gram calories per square
centimeter Of body surface. continued
for several days, has been depressed
from Is to 90 per cent and has stayed
down three or four weeks after the
final treatment. ,
There Is still much confusion, DR..
LaurenS said, about the action 2of light
cases of anemia. Persons in poorly
lighted rooms grow pale, but are not
necessarily anemic and may have. a
good ratio of red blood cells. Light,
however, may increase the red blood
cells. Soon after the irradiation treat
'HAent, Or. Laurens said, there is an
actual decrease in all the formed ele-
ments Of .the blood-the white and red
blood cells and the flagellae-and an
increase In volume Of the blood plaSma.
Manufactures Vitamins.
An important effect of ultra violet
radiation, he pointed out, was the
manufacture in, the body Of the mys-
tance In the building process of the
bones and teeth, and absence of which
causes ricketS and other diseases Of
children. It is essential, however, to
have this vitamin in the diet In such
forms as cod liver oil, and irradiation
OF the body will not make up for a
dietary deficiency. Some food sub
stances. he pointed out. can be endowed
with vitamin D by irradiation. Thus
the irradiation of nursing mother has
a good effect on the milk. The func-
ton of this vitamin, he said, apparently
was to keep up the calcium phosphorus
balance in the body Thus the alb
corption Of calcium necessary for bone
building depends on the proper acidity
of the blood, and vitamin D deficiency
tends to increase the blood akalinity.
There Is some question, DR.. Laurens
said, as to what part of the spectrum
Is most effective. Some experiments
now tend to show that the normal
growth and mineral metabolism of
chickens depends upon the whole spec
trum rather than the ultraviolet. Dr.
Laurens warned against the popular use
of violet ray lamps unless such treat
rf1ent Is prescribed by physician who
understands light therapy. He said that
such treatment is likely to have dan
gerous effects on the eyes,, is extremely
bad for fever patients, and Is likely to
do great deal OF damage to cases Of
low blood pressure and to persons with
skins which are easily burned.
Workers at the Bureau of Standards
described conditions due to careleSSnesS
In experimenting with ultra violet rays
in which the person Is awakened by
excruciating pain In the eyes In the
middle of the night, finds the eyes glued
together and experiences intense pain
when he tries to open them; next day
the eyes are greatly inflamed and 1t Is
extremely painful to accommodate them
to reading or any similar occupation. In
few days the condition clears up.
No Permanent Damage.
1t is unlikely that any permanent
damage is done, Dr. Laurens said, since
the retina is not injured. Cataracts
have been attributed. 1t was pointed
out, to both ultraviolet and infra
neutrality-suspicious. to the infra-
red Just below the visible spectrum.
Recent experiments showing the be-
havior of plants under diverse light ex-
posures were described by DR.. John M.
Arthur OF. the Boyce Thompson Insti-
tute of Yonkers, N. Y. Plants grown in
open sunlight we're kept as controls over