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us what he has learned from the study of his material.He has approached his subject with an unbiasedmind and, after careful consideration of the con-

tending views, has been driven to the conclusion thatthe melanomata are epithelial tumours, the result ofpost-embryonic, pathological attempts at the con-

version of epithelium into mesenchyme, attempts thatare often crowned with success. The idea is not new.It was propounded nearly 40 years ago by KROMAYER,UNNA, and others, and has since then gained an

ever-increasing number of adherents. Dr. Dawsorr’smaterial is rich and well digested. His illustrationsare admirable, and unlike so many morbid anatomistshe realises that they form the surest proof of hisarguments. His conclusions fall into two groups.He shows that the pigment melanin is producedsolely by the epithelial cells of the ectoderm-i.e.,the epidermis and its appendages and the centralnervous system. True " melanoblasts " are epithelialcells which may, however, enter the deep tissues.

They are distinct from the mesenchymas " chromato-phores " which ingest the pigment by phagocyticaction but do not produce it. He traces the formationof the " naevus " cells from the epithelium in cutaneousmoles and the melanotic tumours which arise in them.With the help of beautiful drawings he shows theextreme polymorphism that the cells of these tumoursassume and that the melano-carcinomata, -sarcomata,- fibro-sarcomata, &c., are but different forms of thesame tumour. He concludes that even the most" sarcomatous" melanomata are epithelial tumoursand extends this conclusion to the ocular melanomata.It is to be regretted, for the sake of completeness,that he does not deal more fully with the rare

recorded instances of melanomata of other parts ofthe body. Dr. DAWSON does not go so far as KROMAYERand admit a complete " desmoplasia " (or assumptionof all the characters of connective tissue) of epithelialcells. He is perhaps wise not to do so. His paper isa valuable contribution to the question of the speci-ficity of the germinal layers, which will have to beconsidered not only by pathologists but by generalbiologists.

A CONQUEROR OF INSECT PESTS.Prof. MAXWELL LEFROY, whose obituary notice

appears on another page, was perhaps the foremosteconomic entomologist in the British Empire. In thecourse of his career he had three really spectacularsuccesses. The first was when he went to the WestIndies. The sugar-cane, on which the prosperity ofthe islands depended, was being destroyed by a beetlewhich bored into the stems. LEFROY discovered thatthe eggs of this insect were laid on the backs of theleaves ; he described the appearance of the egg-clusters, and small native boys were employed to

scrape them off the leaves and the sugar-cane cropwas saved. When he arrived in India the corn cropsin certain districts were being devastated by a plagueof locusts. The seriousness of the situation may bejudged from the fact that the crop reaped was only25 per cent. of the normal yield, and in India, wherethe peasant proprietors live close to the margin ofsubsistence, there was imminent danger of famine.LEFROY discovered that the locusts kept flying aboutthe same locality until the rains came and softenedthe ground ; they then descended to the ground andlaid their eggs in holes bored in the earth. Once the

period of oviposition was determined, it was easy tocalculate when the wingless young (nymphs) wouldhatch out, and LEFROY constructed what may betermed shrimping-nets out of light bamboo and sent

the native boys with them through the growing corn,with the result that the young locusts were capturedby the sackful and the next year’s crop was normal.Lastly, when lie was sent to Australia in the latter

part of the war he had also a very serious situation todeal with. The Imperial Government had purchasedlargo amounts of Australian wheat which was storedin Australia whore it was being rapidly destroyed byweevils. LEFROY discovered that the wheat was

contained in sacks which were piled on the groundcovered with insufficient roofing and inadequatelyprotected against rain and damp. The lowest bagsburst and the grain exuded and thus easy accesswas afforded to the weevils. LEFROY found that the

grain weevil was an insect which had lost the use ofits wings and that it always began its attacks byentering grain lying on the ground, so he directedthat the grain should be housed in sheds providedwith an adequate flooring raised two or three feetabove the ground and that the soil beneath themshould be treated with disinfectants such as naphtha-lene. These measures were entirely successful in

stemming the weevil plague. LEFROY always insistedon the importance of studying insects in the openunder natural conditions. Quite early in his careerhe laid down the thesis that to attack an insect pestsuccessfully its whole life-history must be studied;then the weak links in its chain of developmentalstages would be discovered where the attack could besuccessfully pressed home. Whilst he recognised theimportance of a knowledge of their structure, whichis as indispensable a pre-requisite as the study ofgrammar in learning a language, he maintained thatall further knowledge should be gathered in the field." One must live with insects," he said, " in order toknow them."

VACCINIA AND VARIOLA VIRUSES.THE ultramicroscopic viruses are notoriously

difficult to study, for obstacles, in some cases

seemingly insurmountable, are encountered by what-ever avenue the territory of these smallest of

living creatures is approached. Too small to be

directly visible with the microscope, difficult to

cultivate, ana, even 11 cuitivaoie, witnout clistinctive

reactions, we have been left only with the crude testof demonstrating their presence by inoculation of a

bacteria-free filtrate into living animals. Filtrationand inoculation experiments, depending as they doon such variable factors as the construction of thefilter and susceptibility of the animal, have nothitherto encouraged accurate quantitative work.Perhaps some entirely new method of approach mustbe discovered before these ultramicroscopic virusescan be scientifically classified. In this connexion itis instructive to notice that Dr. Mervyn Gordon, inhis studies on the viruses of vaccinia and variola(summarised in our last issue), has departed from theconventional technique of bacteriological examination,for we read practically nothing in his report ofattempts to see these viruses with the microscope,or to stain them, or even to cultivate them in thecustomary fashion. He has relied entirely on experi-mental work on animals and is to be congratulatedon having succeeded in introducing more accurate

quantitative methods of analysis. He found theshaved skin of the rabbit a delicate indicator for

vaccinia virus and devised methods for measuring theminimal vaccinial dose, and has made a careful studyof the properties of antivaccinial serum by quantitative

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means. The most sensitive test for the presence ofvaccinia virus is undoubtedly the cutaneous test ofvirulence, but the complement-fixation and agglutina-tion tests, though their range is shorter, are not lackingin specificity, and, since they provide an independentmeasure, they form a welcome addition to our

armamentarium. The special feature of Dr. Gordon’swork is the successful employment of serologicalmethods, which has been made possible by employinghomologous (rabbit) pulp as a virus, and the proofthat complement fixation and agglutination occur

with vaccinia virus in much the same way as with

pathogenic bacteria brings vaccinia into line with thelatter group. The experiment in which an immunisedserum produced a definite immunity are also ofinterest.Some of the experiments which Dr. Gordon reports

in the permeability of various surfaces of the rabbit tothe virus of vaccinia raise the question whether themain natural method of spread of this bovine diseasemay not be in part by the respiratory tract ratherthan by fortuitous cutaneous inoculation as hithertosupposed. He found the most certain wny of intro-

ducing the vaccinial virus to be by scarification ofthe skin, but in the absence of mechanical injury themost susceptible and permeable of the surfaces ofthe rabbit seems to be the nasal mucous membrane.When vaccinia virus gains access to the nasal mucosa,after an incubation period of six to eight days, acondition of acute nasal catarrh develops, accompaniedby a muco-purulent nasal discharge which at theonset contains the virus of vaccinia in abundance.Animals thus infected became immune to vaccinia.

Confirmatory evidence of the capacity of the nasalmucosa to absorb antigen was furnished by controlobservations in which the application of killedB. coli to the mucous membrane of the nose wasfollowed by the appearance of specific antibodies tothat micro-organism in the blood. He observes thatthe limits of this physiological property of the nasalmucosa and the degree to which it can be exploitedfor prophylactic purposes have still to be determined.The acute attack of nasal catarrh which follows afteran incubation period when the vaccinial virus hasgained access to the nasal mucous membrane links upthe disease which we call vaccinia to the group ofinfluenza and the common cold. It is important thatwe should obtain further information on the naturaldistribution and mode of spread of vaccinia virus inthe animal kingdom. Thanks to the accurate analysiswhich Dr. Gordon has made we now possess a tripleindex-namely, the cutaneous virulence test, theagglutination, and complement-fixation tests, where-with to identify the presence of vaccinia virus and toestimate its abundance.A point of great practical importance demands a

word of emphasis. Dr. Gordon found when studyingseven different kinds of calf lymph in use in thiscountry for purposes of vaccination that these variedvery greatly in their potency. Some were active at adilution of 1 in 100,000 and others only at a dilution of1 in 100 or even 1 in 10. Since calf lymph is known todeteriorate on keeping it would have been interestingto know something more of the history, particularlythe age, of the samples examined. No information onthis point is given in the report, but as the facts arepresented they seem to suggest that a very significantand inexcusable variation exists in commercial samplesof calf lymph. Obviously this is a question whichrequires official attention. A further feature of Dr.Gordon’s work which has practical implications ishis research on the comparative value against vacciniaof disinfectants. The striking powers of potassiumpermanganate which he reveals should encourage itsuse in small-pox, which has hitherto been largelyempirical.

Annotations.

THE CATARRHAL CHILD.

" Ne quid nimis.

THK importance of catarrhal conditions in childhoodin laying the foundations of future disease has receiveda greatly increased measure of recognition duringthe present year. This recognition is evidenced bythe appearance of several contributions to medicalliterature which show not only that podiatrists of highstanding in medical practice and in the public serviceshave given their serious attention to the subject,but that their observations have led them to differ in

important respects from many of the earlier accountsof catarrhal states. A notable instance of this differ-ence is to be found in the age which is regarded astypical for the onset of catarrh. The " catarrhal

child," as hitherto depicted, is usually in the secondyear of life, or older, and presents features which areeither typical or suggestive of rickets ; by manywriters the catarrhal symptoms have been regardedas essential manifestations of rickets, the causativefactors being, at any rate, nutritional and environ-mental. The article by Dr. R. C. Clarke, which appearsin our present issue, introduces some striking modifica-tions of this conception of the aetiology and incidenceof catarrh. According to his account, respiratorycatarrh is extremely common in the first few weeks oflife, being present in as many as 50 per cent. of theinfants which he examined. He has frequently notedthe presence of Harrison’s sulcus in young infants,and regards it as evidence, not of rickets, but of nasalobstruction consequent upon catarrh ; he bases thediagnosis of respiratory catarrh on this sign in con-junction with snuffles and bronchial rales. In earlyinfancy nasal catarrh is almost always accompaniedby bronchial catarrh, whereas in late infancy themajority escape this complication, hence the primeimportance of protecting the infant from infectionduring the first three or four months. Dr. H. K.Waller, in a memorandum on the catarrhal child,which appeared in the recent report of Sir GeorgeNewman to the Minister of Health, gives a descriptionof this type of case, which is in many respects in closeagreement with the views expressed by Dr. Clarke.The prevalence of catarrh in the first weeks of life isemphasised, as are also the interference with efficientsucking, and hence with nutrition, the development of" tonsils and adenoids," and the increased suscepti-bility to febrile attacks and to infection with pyogenicorganisms. Both Dr. Clarke and Dr. Waller lay stress-on the necessity of protecting the infant from catarrhalorganisms, and recommend as the most useful measure-for this purpose the use of a mask or folded hand-kerchief by the mother or nurse who is attending tothe child. On the more speculative problem of aetiologythe agreement between the two articles is less complete.The traditional association between rickets and catarrhmust necessarily be called in question by those whoregard the latter as an ailment of early infancy. Dr.Clarke does not discuss this point; Dr. Waller meetsit with a suggestion which inverts the hithertoestablished view of the causal sequence. " The rachiticchild’s tendency to febrile reactions has been fre-quently described. It is possible that the catarrhaldiathesis has been overlooked as a predisposing factorin producing rickets." A further question inevitablyarises if the typical age-incidence of a morbid state isfound in the first weeks of life : Does heredity playa part in the aetiology: Dr. Clarke answers thisdecidedly in the negative : Dr. Waller gives cautiousexpression to the idea that a hereditary element islikely. Should both Dr. Waller’s suggestions receivefurther elaboration, he may provide one more complica-tion to the vexed problem of the aetiology of rickets.