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recognise that no really satistactory method exists

for pinpointing in animals the factors that predisposeto death from coronary artery disease in man. Thesection of the guidelines concerned with the use ofadditives is more dubious. The committee proposesto draw up a permitted list of additives based on long-term surveys of pipe smokers, on the experience inother countries with additives in cigarettes, and ontoxicity tests. There will also be a prohibited list. Thecommittee is taking on a colossal task, particularly withthe volatile flavouring agents which often consist ofmixtures of large numbers of constituents each presentin trace amounts. Is the committee aware, too, thatchemicals such as plasticisers may get into smoke as aresult of the way cigarette filters are made ?

Since it has no statutory authority, the HunterCommittee recommends the Secretary of State to

obtain assurances from any company proposing tomarket, in the United Kingdom, a product containinga tobacco substitute that it will abide by the guidelines.It is to be hoped that this proposed voluntary systemwill work efficiently and be seen to do so. At present,for those who cannot or are unwilling to quit thecigarette habit, the progressive introduction of substi-tutes which produce little tar and tar which is claimedto be less carcinogenic for mouse skin than tobaccotar 10,11 offers the best prospect for the future. Butsomewhere along the line of increasing the proportionof substitute in the substitute-tobacco blend it will be

necessary to add flavours and possibly nicotine for theproduct to be acceptable. A cautious start has beenmade to making this possible.

HAIR DYES AND CANCER

IN carcinogenicity experiments laboratory animalsare customarily fed, injected, or painted with thechemical under test and then observed for the rest oftheir lifespan for any increase in tumour incidencecompared with controls. Such experiments are lengthyand highly expensive, and can cope with only smallnumbers of chemicals. The possibility that manycancers in man may be due to synthetic chemicalsintroduced into the environment has highlighted theneed for much more rapid and inexpensive test sys-tems. One of the most promising new tests measuresthe ability of chemicals to induce revertant mutation in,for example, histidine-requiring bacterial mutants.

Tests of this sort can give results in a matter of daysand can be used to screen large numbers of com-pounds. Their validity depends on the assumptionthat most carcinogens are also mutagens. Already intests. using known carcinogens and harmless analoguesa very high correlation has been found between muta-genicity and carcinogenicity. 12 This finding is suppor-ted by fundamental investigations on the mechanismof action of many carcinogens which show that all areelectrophilic reactants or can be converted by meta-bolism into such agents. - These reactive chemicals caninteract extensively with D.N.A., which may be thetarget site for both carcinogenic and mutagenic10. Hall, R. A., Furlong, R. A. Chemical Engineering, Nov. 11,

1974, p. 90.11. Farley, C. General Practitioner, Sept. 13, 1974, p. 18.12. Ames, B. N., Durston, W. E., Yamasaki, E., Lee, F. D. Proc. natn.

Acad. Sci., U.S.A. 1973, 70, 2281.

effects and so account for the close correlation betweenthe two properties.Work carried out independently in the United States

and England 13,14 using the bacterial mutant system(together with mammalian microsomes to convert

pro-drugs to their active form) has shown that thegreat majority of semipermanent hair dyes are muta-genic in their own right or can be converted to muta-gens by liver microsomes. Thus these agents, whichare known to be absorbed through the skin, must beregarded as potential carcinogens in man. This is acontroversial observation, since earlier tests usingdogs and rodents have not implicated hair dyes as

carcinogens, although there is some preliminaryepidemiological evidence of a higher incidence of lungcancer in beauticians. On p. 226 Dr Searle and hiscolleagues say that their carcinogenicity tests in mice" could indicate some activity ". These observationsare a far cry from the reported statement that hairdyes may carry the same high risk as cigarette smoking.This is speculation, but the convincing evidenceassociating bacterial mutagenicity with carcinogenicitycannot be discounted. Obviously there is urgent needfor a thorough re-evaluation of the toxicology andcarcinogenicity of hair-colourant constituents usingall available methods. Among other things, this

controversy may establish, once and for all, whetherthe bacterial system is a reliable screening method forpotential carcinogens.

DISINFECTANTS AGAINST SQUALOR

SQUALID conditions may necessitate squalid measures.Although it is convenient and safe to deal with urinalseither by using disposables or by employing an

efficient washer/steriliser, these metbods are often

judged to be too expensive. Thus, all too often, theroutine is soaking in tanks or baths of disinfectant.Where this potentially, dangerous procedure must beused, it is clearly important to use the right disinfectantin the right way. Some years ago Christie 15 describeda system using a clear soluble phenolic fluid, withregular topping up between changes, which stood upto microbiological testing. Now Dr Emmerson andMrs Franks (p. 232) report another trial of the samemethod (using a less expensive product) which waswell controlled both microbiologically and by chemicalanalysis.

It is unfortunate that such practices are still in usein Britain; but, while they are, it is important thatdisinfectants should be correctly chosen, purchased,and used. Although much has been written about theuse of disinfectants, there has been too long a delay inoffering official advice about the selection and purchaseof specific products. There are indications, however,that such advice may before long be made available tothose who need it. This, if heeded, will avoid confusion,ensure the use of effective disinfectants, and sparereaders of medical journals the chore of readingtoo many articles on this subject.13. Searle, C. E., Harnden, D. G., Venitt, S., Gyde, O. H. B. Nature,

1975, 255, 506.14. Ames, B. N., Kammen, H. O., Yamasaki, E. Proc. natn. Acad. Sci.,

U.S.A. 1975, 72, 2433.15. Christie, D. R. Lancet, 1967, i, 112.