970

(except in the rare cases where a prisoner has becomeinsane since conviction), and the spectacle of so manydeath sentences pronounced but never carried intoeffect, are in themselves a sure sign that all is notwell with the law as it stands. It may have somethingto learn from the practice of other countries.

1. Burnet, F. M., Fraser, K. B., Lind, P. E. Nature, Lond. 1953,171, 163.

2. Burner, F. M., Lind, P. E. Symposia on Quantitative Biology,Cold Spring Harbor, New York. 1953 ; vol. 18, p. 21.

3. Hirst, G. K., Gottlieb, T. E. J. exp. Med. 1953, 98, 41.4. Burnet, F. M., Lind, P. E. Nature, Lond. 1954, 173, 627.

Annotations

A SURGICAL OCCASION

As we have already announced, the American Collegeof Surgeons is, for the first time, holding one of itssectional meetings in England, and the proceedingswhich will open at the Royal College of Surgeons onMay 17, with Sir Cecil Wakeley in the chair, are likelyto be attended by some 400 American and 600 Britishsurgeons. The three-day programme, which promisescontributions from some 70 speakers, includes " paneldiscussions" on intestinal obstruction, on preoperativeand postoperative care, on massive haemorrhage fromthe gastro-intestinal tract, and on hand surgery, togetherwith symposia on gyn2ecological subjects, on cancer, andon cardiovascular surgery ; while official lectures in theRoyal College of Surgeons will be given by Prof. HowardC. Naffziger (progressive exophthalmos) and Prof.Walter C. MacKenzie (pancreatitis). Local arrangementsmade by the English college include visits to Londonhospitals for operating sessions, special programmes forurologists, ophthalmologists, and otolaryngologists, andan exhibition of surgical instruments. There will be abanquet at the Dorchester Hotel, with the Marquess ofSalisbury as the guest of honour, and receptions by thepresident and council of the Royal College of Surgeons,and by H.M. Government. The new great hall of thecollege, with a seating capacity of about 700, will be usedfor the meeting.

After arriving in England next week, many of theAmerican visitors will participate in the meeting of theAssociation of Surgeons of Great Britain and Irelandwhich is being held in Leeds from May 13 to 15.. TheRoyal College of Surgeons of Edinburgh, where Prof.Evarts A. Graham is to deliver the Fraser lecture, is

holding’a reception on May 11 ; and both before and afterthe London meetings visits will be paid by groups ofindividuals to various centres in this country and tofurther conferences on the Continent.

VIRUS VIRULENCE

THE researches of Burnet and his colleagues 1 2 inMelbourne and Hirst and Gottlieb s in New York haveclearly shown that when two different strains of influenzavirus are grown together, under conditions in whichboth can infect the same cells, new forms of virus areproduced which carry properties from both parents.There is still doubt as to the finer details of how thesecombined forms of virus are brought into being, butmeanwhile Burnet and Lind 4 have used the genetics ofthe interaction between two influenza viruses to studythe problem of virus virulence.

All strains of influenza virus grow well in the chickembryo, but some kill the chick rapidly by producinghaemorrhagio lesions. Again, all strains of influenza virusA grow in the mouse lung ; most strains do not producepneumonia, but by adaptation these strains can be trainedto cause fatal pneumonia. Likewise, one or two strainsof influenza-A virus have been adapted to produce fatalencephalitis on inoculation into the mouse brain. It is

possible therefore to have avirulent influenza strains

and strains which are virulent in one or more of threedifferent situations, and to study the effects of geneticinteraction between avirulent and virulent strains.Burnet and Lind 4 summarise the results of many experi.ments with the finding that the progeny of crosses of thistype generally show many intermediate stages of virulence.This, they point out, accords with the gradual way inwhich virulence of a virus for a new host is built up bypassage, and it suggests that the virulence of a strainis a function of several genes. It is still uncertain howthese genes are shared between parents and progenyduring the simultaneous multiplication of an avirulentand a virulent strain in the same cell, but Burnet andLind postulate the existence of virulence genes ratherloosely associated with the rest of the " nuclear " appara-tus (or genome) of the virus and able to multiply in thehost-cell in a rather independent way. Different genomeswill have different affinities for these virulence genes,and the two will reassociate at a later stage in virusmultiplication.

This type of hypothesis reflects the very rapid progressin the theoretical understanding of the multiplication ofthese viruses. But the concept of virulence is not aneasy one, being inseparable from its counterpart-thesusceptibility of the host. Virulence may embody anumber of components : the rate of virus multiplication,the amount of virus produced, the possible toxic materialsproduced, and interference with normal cellular syn-theses. Future study will probably be directed to theway in which these and other components are inheritedalong with the general over-all property of virulence.meanwhile studies such as those of Burnet and Lindcarry wider implications, and should stimulate fresh ideason the biology of living cells.

THE NEW EPIDEMIOLOGY

BECAUSE of their apparent preoccupation with thework of Snow on cholera, epidemiologists are oftenaccused of having a

" Broad Street pump fixation." That

charge could not be levelled against Dr. John Gordon,whose views on population problems we noted in a

leading article last week. As he said to a meeting of theepidemiology section of the Royal Society of Medicineon April 30, epidemiology is an attitude of mind ratherthan a body of knowledge, a research discipline now widelyapplied over the whole field of medicine. Unlike the otherbasic methods of medical investigation-clinical ancl

laboratory study-it is concerned with groups ratherthan with individuals, and Gordon believes that it canplay a useful and complementary role in the study of theaetiology of disease.

Originally, epidemiologists functioned as a fire-brigade,dealing in a patchwork way with dramatic outbreaks ofacute infectious illness. Later, by a process of learningwhile doing (what would now be called operationalresearch), the careful recording and analysis of thesequence of events in a series of outbreaks allowed the

generalisation of principles of epidemic behaviour. Evennow, the epidemiologist learns his trade by the study ofinfectious illness. Although still important in theWestern world and still dominating all else in manyother countries, infections are being supplanted by -thedegenerative diseases as a cause of death and disability.Some of the old techniques retain their value, but withdisorders which evolve slowly, both in the individual andin the community, new ideas are required. The probandmethod is the only really short cut to a study of thefactors which affect the natural history of a disease:essentially, this means the comparison of the past historyof known cases of the disease with similar histories forcontrol subjects ; the inference is that any differencesobserved in habit or physical constitution are factors inthe causation of disease. Useful as it is in giving clues,this approach has its limitations since we can never be