experiences, the normal protective barriers that kept mutagenic agents from the inte rnal
organs have been more and more fre quently penetrated.’
The s tudy of human chromos omes is in its infancy, and s o it has only recently become pos s ible
to s tudy the effect of environme ntal factors upon the m. It was not until 1956 that new
techniques made it pos s ible to determine accurately the number of chromos omes in the
human cell—46—and to obs erve them in s uch detail that the pres ence or abs ence of whole
chromos omes or even parts of chromos omes could be detected. The whole concept of genetic
damage by s omething in the environment is als o relatively new, and is little unders tood except
by the geneticists , whos e advice is too seldom sought. The hazard from radiation in its various
forms is now reas onably well unders tood—although s till denied in surprising places. Dr. Muller
has frequently had occas ion to depl ore the ‘res is tance to the acceptance of genetic pri nciples
on the part of s o many, not only of governme ntal appointees in the policy-making positions,
but als o of s o many of the medical profession.’ The fact that chemicals may play a role similar
to radiation has scarcely dawned on the public mind, nor on the minds of mos t medical or
scientific workers. For this reason the role of chemicals in general use (rather tha n in laboratory
experime nts ) has not yet been ass ess ed. It is extremely important that this be done.
Sir Macfarlane is not alone in his estimate of the potential danger. Dr. Peter Alexander, an
outs tanding Britis h authority, has said that the radiomimetic chemicals ‘may well represent a
greater danger’ than radiation. Dr. Muller, with the pers pective gained by decades of
dis tinguis hed work in genetics , warns that various chemicals (including groups repres ente d by
pesticides) ‘can raise the mutation frequency as much as radiation...As yet far too little is
known of the extent to which our genes , under mode rn conditions of expos ure to unus ual
chemicals , are being s ubjected to s uch mutagenic influences .’
The wides pread neglect of the problem of che mical mutagens is perhaps due to the fact that
thos e firs t dis covered we re of scientific interest only. Nitrogen mustard, after all, is not sprayed
upon whole populations from the air; its us e is in the hands of experimental biologists or of
phys icians who us e it in cancer therapy. (A cas e of chromos ome da mage in a patient receiving
s uch therapy has recently been re porte d.) But ins ecticides and weed killers are brought into
intimate contact with large numbe rs of people. Des pite the s cant atte ntion that has been given
to the matter, it is possible to assemble specific information on a numbe r of thes e pes ticides ,
s howing that they dis turb the cell’s vital proces s es in ways ranging from s light chromos ome
damage to gene mutation, and with cons equences extending to the ultimate dis as ter of
malignancy. Mos quitoes expos ed to DDT for s everal generations turned into s trange creatures
called gynandromorphs—pa rt ma le and part female.
Plants treated with various phenols s uffered profound des truction of chromos omes , changes in
genes , a s triking numbe r of mutations , ‘irrevers ible hereditary changes ’. Mutations als o
occurred in fruit flies , the class ic s ubject of genetics experiments , when s ubjected to phenol;
thes e flies developed mutations s o damaging as to be fatal on expos ure to one of the common
herbicides or to urethane. U rethane belongs to the group of c hemicals called carbamates , from
which an increas ing numbe r of insecticides and other agricultural chemicals are drawn. Two of
the carbamates are actually us ed to prevent s prouting of potatoes in s torage—precisely
becaus e of their proven effect in s topping cell divis ion. Another antis prouting agent, maleic
hydrazide, is rated a powerful mutagen. Plants treated with benze ne hexachloride (BHC) or
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