802

most suitable ; and a crystal microphone with a metaldiaphragm was recommended as being stable under

varying atmospheric conditions and as giving the

required performance. Small crystal insert receiversare given a word of special commendation, but the com-mittee’s aid is designed for both this type and the earcaptype. The receiver.with a flat earcap advocated in the

report is a modification of a miniature unit developedoriginally for the Fighting Forces ; it weighs aboutan ounce. The battery replacement cost, according to thereport, is about 1.1d. per hour of actual use with theexternal receiver type of aid ; while with the insertreceiver aid the running cost is about 0.6d. per hour.

FUMIGATION WITH METHYL BROMIDE

METHYL bromide is mainly used as a refrigerant, as afire-extinguisher, and as a methylating agent. Recentlyit has become popular as a fumigant of ships, warehouses,and other premises to control insect pests, and in thisconnexion fatalities and poisonings have been reported.The chemical being highly toxic to human beings aswell as to insects, the Home Office has issued a

useful pamphlet 1 on the risks and precautionarymeasures.

Methyl bromide boils at a low temperature (45°C)and it is therefore usually distributed under slight pressurein cylinders containing the liquid, contact with whichmay cause severe blistering. Clothing contaminatedwith the liquid should instantly be removed because ahigh concentration of gas can arise from it. The gas isheavier than air and has greater powers of penetrationthrough walls and sealing material than other commonfumigants such as hydrogen cyanide or ethylene oxide.Deaths have resulted both from exposure to high concen-trations of the gas and also from continued exposure tolow concentrations. The gas is insidious because it has

only a faint odour and also because the symptoms afterexposure may be delayed for a day or more. The symp-toms of poisoning are mainly referable to the nervoussystem and include headache, dizziness, diplopia,vomiting, and lethargy, with later convulsions and

collapse. -

The precautions taken should be at least as rigid asthose taken when HCN is used, and it is recommendedthat a pungent lacrimatory gas such as chloropicrin (5%)should be added to methyl bromide so that its presencein the air can easily be detected.In addition, all apparatus used for the delivery of methyl

bromide gas into rooms should be tested before being usedin practical operations. The halide detector lamp is recom-mended for detecting low concentrations of methyl bromidein the atmosphere. These lamps vary in sensitivity to the gas,some types probably not being sensitive enough to detect17 parts per million of methyl bromide, the figure givenas the upper limit of safe concentration. Advice on suitable

types can be obtained from the director of the Pest InfestationLaboratory at Slough. It is desirable that the people carryingout fumigation operations should be given practical demon-strations of the performance of the lamps in known concen-trations of methyl bromide. The lamps should be used todetect leaks at the time of fumigation, during the exposureperiod, and before a clearance certificate is issued.

Each operator or other person entering the space underfumigation must be provided with a protective apparatusof proved efficiency against methyl bromide. In highconcentrations of the gas a self-contained (oxygen-generating) or a positive-pressure air-breathing apparatusis necessary, but in low concentrations canister respira-tors of an appropriate type may be used.

Before fumigation, rooms and other spaces should besealed with an impervious material which should be ofan even higher standard than for fumigations by HCN1. Fumigation with Methyl Bromide. H.M. Stationery Office.

June, 1947. Pp. 8. 2d.

or ethylene oxide. All rooms, compartments, and alley-ways with walls common to those of the area to be

fumigated should be evacuated, and warning noticesshould be affixed. Fumigation staffs should consist of atleast two persons, and one of them at least should be inattendance throughout the fumigation and airing period.Both persons should have adequate colour-vision andshould be trained in the use of protective and detectorapparatus and in first-aid. The dose of methyl bromideshould be injected from cylinders placed outside thefumigation area. Airing should be conducted and con-cluded before the entry of any person other than theoperators, who should work in pairs and wear theirrespirators until tests show that the concentration of gasis a safe one. At this stage a preliminary certificate ofclearance is to be issued and the fumigated area closedagain for a period to guard against the risk of dangerousquantities of gas being subsequently evolved fromabsorbent material. A final certificate of clearanceshould not be given until thorough tests have been made.Ships should never be fumigated until all persons havebeen taken off, and special care should be taken to testthe air in the holds before a clearance certificate is issued.

TELEVISION IN SURGICAL OPERATIONS

LAST February surgical operations were televisedfor the first time at the Johns Hopkins Hospital, Balti-more.! One camera was fixed 41/2ft. above the operating-table, and the image was so sharp that the numbers ona dollar bill placed on the table could be clearly read onthe projection screens. A second camera was installedin the gallery to give a general view of the theatre ;and the surgeon provided a running commentary througha microphone. The experiment is said to have provedconclusively that demonstration of operations to a

group of more than three or four is best effected bytelevision, even though, for the moment, reproductionis only in black-and-white.

BRITAIN’S HEALTH

THE results of the medical examination of men andwomen called to the colours in 1939-46 are summarisedin a report from the Ministry of Labour and NationalService.2 It will be remembered that grades i and 11

were deemed fit for military service, while grades ill

and iv were not. Grade iia consisted of those who,though fit for service, were handicapped by defects ofvisual acuity or by deformity of the feet. Of the

3,240,906 youths under 21, 91 % fell into grades i and n,and 9% into grades 111 and iv ; and of the age-group21-25 (1,085,908 men) 85% were fit and 15% unfit.At ages 26-35 (2,045,480 men) the percentages were79 and 21, and at 36-45 (805,480 men) they were 65and 35. One should be careful in using these figures asa basis for conclusions about the health of the countryas a whole, for the scale is heavily weighted at the

younger end, where one would expect to find the majorityin good health. It is perhaps encouraging, however, thatof the relatively few men over the age of 36 the proportionadjudged fit for service was as high as 65%.Women examined numbered 550,486-less than a

tenth of the total of men. They were volunteers inthe sense that they preferred joining the Forces to

entering industry, and as might therefore be expectedthey had a rather better health bill than the men,though the difference in the proportions accepted andthose refused was not great. Among the men eyetrouble and foot trouble were about equally prevalent,but in the women deformities of the feet were notednearly five times as often as defects in visual acuity.1. Trimble, I. R., Reese, F. M. Bull. Johns Hopk. Hosp. 1947, 81,

186.2. Report of the Ministry for 1939-46. Cmd. 7225. H.M. Stationery

Office. Pp. 394. 7s.