Evening star., 1938-02-08
How did the sIoth get that way?

How did the sIoth get that way?
AS the name indicates, he is about the
most lifeless OF warm-blooded animals
and has become . symbol of extreme
laziness. And yet he does not belong to
particularly primitive group. He is
one Of the progressive "placentals," like
mice, monkeys and men, that have be-
come the dominant form of life on the
planet. He is far removed from really
primitive mammals. like the opposum or
the egg-laying platypus of New Zealand,
which are not SO far removed from their
reptile ancestry.
Nor is the sloth cursed with an espe-
cially inert ancestry. One of his family,
the great sloth, was an enormous crea-
ture which once lived around the District
of Columbia and must have been almost
the dominant form of life in his day.
He couldn't stand the transition from
the ice age and became extinct-prob-
ably about the time man made his first
appearance on this continent.
And how did the monkey get that way?
He belongs at the opposite extreme
a member of the most progressive branch
active and driven by curiosity. traits ex-
emplified in their greatest development
by the dominant member OF the monkey
family-man. Monkey and sloth started
out from about the same place. What is
responsible for the difference?
That is the question which DR.. Sidney
w. Britton, professor of physiology at
the University of Virginia, is seeking to
answer. He left Charlottesville yesterday
for stay of several months at Barro
Colorado Island in Gatun Lake, Canal
Zone, taking with him extracts of the
adrenal, thyroid and pituitary glands.
He will inject these into monkeys, sloths
and other tropical animals and study the
responses.
1t is entirely possible, he believes that
the sloth is chiefly gland" case. Espe-
cially. it seems likely he doesn't have
enough thyroid or adrenal secretions,
which, in such mammals as man, act as
energy whips. Prof. Britton has been
especially concerned for the past few
years in studying the effects of cortin,
the secretion from the cortex of the
adrenal glands, which Is essential to life
ana serves also as great energy pro-
ducer
OAAS ASuoOAA WHY VIC SlOLll Is SD lazy Is
quite apparent. He hasn't much muscle
less than half as much, in fact, as most
other mammals Of the same size and
weight. Even If he had impulses to do
much he wouldn't have the muscles
to respond to those impulses. But this
Is probably a secondary cause. The
muscles may have been lost In the first
place through lack Of use. This Is much
the same condition as that encountered
by q person who leaves bed for the first
time after long illness. He is sur
prised to find that he can't stand up
The leg muscles will not do their job
Physicians recognize that the natural
tendency Of an elderly person to stay
In bed should be discouraged. Such
persons soon reach the point where they
never can get out Of bed again, for their
muscles degenerate. The sloth may be
the result of evolutionary lying xin-bed-
eventually reaching the point where the
muscles not only degenerated but dis
appeared. Now all the poor creature can
do is stay in bed-upside down on the
limb Of jungle tree.
DR.. Britton tried some preliminary ex-
periments during a three-month stay at
Barro Colorado Island last year. He
found that when sloths were given proper
proportions Of endocrine injections they
temporarily became quite active, using
to the utmost the muscles they had. This
year he will try to learn more about the
bodily functions Of the sloth and his
jungle compAnioua Body Temperature