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tasks they are expected to discharge. In future the

"operating-theatre assistants ", as they should be

known, would progress through grades (trainee,qualified, and senior). If, in so doing, they earn theconfidence of other members of the team, they shouldbe allowed to function as scrubbed assistants to the

surgeon.The report may not be accepted everywhere, because

it is concerned with an area in which precedent andtradition are strong. Even those gore-stained frock-coats were not, we have been told, quickly discarded.But its arguments are convincing, and several of itsrecommendations have already become establishedcustoms in some hospitals.

FOOT-AND-MOUTH VIRUS

THERE is not much doubt that foot-and-mouthdisease (F.M.D.) is largely airborne. Man, fomites, andwild animals may play some part in the disseminationof an epidemic (and must not be neglected), but withinthe farm and probably over a wider area, if the atmo-spheric conditions are suitable, airborne spread is therule. The discovery that tissue-cultures of calf thyroidcan be used as sensitive detectors of F.M.D. virus has

permitted the various sources of infection to be com-pared. Infected pigs release more virus than do cowsor sheep, but whereas the greatest dispersal frompigs and cows takes place when the lesions are general-ised, sheep disperse large amounts of the virus beforelesions can be detected, suggesting that in sheep theinitial lesion is in the respiratory tract rather than onthe tongue. Not all strains of virus behave identically,which may indicate some differences in their ability tosurvive in air. In natural epidemics sheep seem lessimportant as a source of infection than other animals.Cows are the commonest victims, maybe because theyinhale a larger volume of infected air and symptomsdevelop mere rapidly.

F.M.D. in man is a great rarity, but those who workwith this virus in the laboratory almost invariably pickit up in their noses.

2 The human nose is, in fact, amore sensitive detector of F.M.D. virus than calf

thyroid tissue and it is a more convenient tool. Fromthe " infected " nose, either on swabs or in blowings,the virus may be recovered by standard methods, butthere is no evidence that it produces any pathologicalchange in this situation. (Most human infections havefollowed an exceptional accident, such as self-inocu-lation.) None of the human detectors have anysymptoms of F.M.D. or a rise in antibody. The concen-tration of virus taken up by the human nose reachesits maximum in about five minutes. If the humandetector moves into a higher concentration of virus,the amount in the nose rises in equilibrium with it. Ina virus-free environment, the amount of virus in thenose falls steadily until it can be detected only in noseblowings. No experiments were done to see whetherthe human carrier can transmit virus to a susceptibleanimal, but on one occasion the virus was transferredto another person in the course of casual conversation.

1. Donaldson, A. I., Herniman, K. A. J., Parker, J., Sellers, R. F.J. Hyg., Camb. 1970, 68, 557.

2. Sellers, R. F., Donaldson, A. I., Herniman, K. A. J. ibid. p. 565.

Industrial, surgical, and paper masks were quite use-less in preventing the entry or dispersal of the virus.Many of these results agree fairly closely with those

obtained at the Common Cold Research Unit withviruses pathogenic to man. 3 The effects of inhalingrhinoviruses (to which F.M.D. may be allied) are muchthe same, except that, having settled on the mucousmembrane, these viruses set up pathological changesand multiply. If it were not for the danger to animalsof economic importance, F.M.D. virus would be a goodmodel for the study of human infection.

INEQUALITY OF LIMB LENGTHIF one arm is longer than the other, the difference

is virtually unnoticeable unless it is extreme. But

discrepancies in leg length of 2-5 cm. or more resultin a bad limp which may be a source of painful self-consciousness to the adolescent or young adult.Differences in length may result from increased

growth due to hemihypertrophy or to local stimulationof epiphyses by osteomyelitis or midshaft fractures.Decreased growth may arise as a congenital mani-festation (affecting the femur most commonly), as

the result of poliomyelitis, or after epiphyseal damagefrom trauma or infection.There are three main approaches to treatment-

namely, leg lengthening, epiphyseal arrest, or shorten-ing of the normal limb. Lengthening is best carriedout in the tibia of a child aged between 8 and 12 years.Gains in length of 2-5-4-5 cm. may be achieved.Epiphyseal arrest and leg shortening both have thedisadvantage of an operation on the normal limb.Growth of the epiphyses of femur and tibia at theknee may be slowed in order to produce limb equalityby the time of skeletal maturity. Accuracy is difficultto achieve, especially when staples are used and thetechnique of epiphyseodesis, as described byPhemister,5 is preferable. This method involves theremoval of a block of bone, traversed by the epi-physeal line, from the medial and -lateral sides of thebone. The epiphyseal line is then curetted and thebone blocks reinserted, having been rotated 180°.

Leg shortening is usually performed on the fullygrown patient, so that the difference in limb length canbe accurately measured. It is also valuable whenchronic sepsis precludes surgery on the affected side.The main disadvantage is that reduction in height ofan already short person may not be acceptable. The

procedure may be applied to both tibia and femur.Muscles readily adapt to removal of extensive seg-ments of bone. A survey of femoral shortening fromthe Mayo Clinic 6 describes the results in 19 patients.The length of bone resected ranged from 3-7 to 12.7cm. Various techniques were used, the commonest(in 9 patients) being subtrochanteric resection of bonewith internal fixation by an intramedullary nail supple-mented by bone-grafts. In 3 cases union was delayed.There is little doubt that, of the three methods,shortening is the simplest and safest.

3. Buckland, F. E., Tyrrell; D. A. J. ibid. 1964, 62, 365.4. Poirier, H. J. Bone Jt Surg. 1968, 50B, 61.5. Phemister, D. B. ibid. 1933, 15, 1.6. Welsh, J. A., Sweeting, R. C., James, J. M. Mayo Clinic Proc. 1971,

46, 29.