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genetic factors but, generally, the conclusion mustbe that breeding from animals that have them-selves survived infection necessarily leads to

results, in succeeding generations, which are

exceedingly difficult to interpret on genetic groundswith assurance. WEBSTER, in his latest experi-ments, has endeavoured to circumvent this difficultyby judging the parents according to the reactionof the progeny, parents whose first litters survivedor succumbed at a chosen rate being selected forthe breeding of further litters, and thus susceptibleor resistant lines being built up. The RockefellerInstitute strain of mice formed the material forthese studies and B. enteritidis was chosen as the

infecting organism. Unselected mice injectedintrastomachally with a standard dose of this

organism suffered a death-rate of 37 per cent."

Susceptible " lines developed from the progenyof mice dying early after infection had death-ratesof approximately 85 per cent., while by breedingfrom unexposed progeny of mice surviving infection46 resistant " lines only 15 per cent. susceptiblewere obtained. In the latter case it must againbe noted that the lines were originally developedfrom surviving animals (carefully selected for non-carriers), while in later generations the parentswere not tested but, as in the susceptible lines,only chosen according to the mortality sufferedby their offspring. Between different strains ofmice very large differences in reaction were alsorevealed. For instance, of 164 white-faced mice89 per cent. succumbed to the standard dose,while of the " Bagg " strain (albino) only 23 percent. died out of the 452 tested. With suchdifferences it should be possible to determine atleast part of the genetic basis of immunity tothis particular infection. WEBSTER, by crossingwhite-face susceptibles with resistant RockefellerInstitute mice, concludes that it is probable thatresistance factors are dominant and not sex-linked,while both he and IRWIN find that weight at

injection was correlated with the percentagemortality; but that in itself cannot be con-

sidered as having contributed more than a minorpart to the differences in mortality observed.An important point with regard to the genetic

factor is the problem of its specificity or non-specificity. In previous papers WEBSTER hasindicated, 7 on the basis of rather small-scale

experiments, that mice that have proved resistantto an infective organism are also resistant to aninjection of a toxic substance such as mercurybichloride. On the other hand, in his observationson the rat IRWIN reports that the incidence to therespiratory infection which is so common among ratcolonies was practically equal among the resistantand susceptible strains. WEBSTER’S latest resultsare somewhat inconclusive. Of four lines of micerelatively susceptible to B. enteritidis three werelikewise susceptible to Pasteurella avicida, B. fried-laenderi, and pneumococcus given intranasally,but the fourth was significantly more resistant.When these organisms were injected intraperi-toneally or intravenously, no significant differences

7 Jour. Exp. Med., 1924, xxxix., 129, and 1925, xlii., 1.

in duration of life of the several lines of micecould be demonstrated. Experiments with loupingill virus showed that of four lines relatively sus-ceptible to B. enteritidis only two were susceptibleto intranasal instillation of the virus, while linesresistant to B. enteritidis also proved relativelysusceptible to the virus infection.

If the genetic factors involved in the productionof individual immunity should prove to be non-specific, generally or even partially, this factshould prove of considerable value in disentanglinginheritance from environment. It should enablethe question of acquired immunity in the offspringto be eliminated, since having bred from thesurvivors to one infection the progeny can b&tested for resistance with another unrelated

organism or even with a toxic substance. Anymethod of attack must, however, as these experi-ments clearly show, be both laborious and time-consuming, and necessitate the use of large-numbers of animals.

PNEUMOTHORAX OR SANATORIUMOR BOTH

THE treatment of pulmonary tuberculosis byartificial pneumothorax has exhibited the sequenceof popularity which seems to be almost the rulein clinical medicine. At first practised with extreme.caution it gradually became of such wide applicationas to be in some institutions almost a routine-

procedure. Now the pendulum has begun to swing-back, and at a meeting of the Tuberculosis Associa-tion recently reported in our columns Dr. F. G.HEAF showed how the treatment was being appliedwithout regard to its limitations and dangers.Some of these misapplications are the penaltiesof a success which has brought with it a readinessto apply the method without first counting theadministrative cost. This cost includes the serviceof radiological and pathological departments, thecomplement of physicians up and down the countryable to continue refills after the patients have leftthe institutions where the pneumothorax was

induced, and long journeys for patients to thenearest refill centre-and the cost has not alwaysbeen visualised. A patient too in the course of this.prolonged treatment may have the refills carriedout by several doctors in turn ; responsibilityis divided and the clinical picture obscured. In

addition, as Dr. HEAF points out, there has been asteady increase in work at all tuberculosis institu-tions of recent years without a correspondingincrease in staff. Twenty years ago fresh air, goodfood, and rest were practically the only ingredientsof treatment; nowadays there are few cases notundergoing some form of special treatment-

collapse therapy, intravenous injections-withadditional calls on the time of the medical and

nursing staffs. Faulty attention to details of

bechnique may easily ensue. The beginner, Dr.HEAF says, is apt to regard the treatment as justputting air into the pleural cavity ; the apparatus.

1 THE LANCET, May 27th, p. 1124.

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is so simple and the needle so easily inserted. Whatis going on inside the thorax is less easily appre-hended ; whether the air is actually causing andmaintaining collapse of the lung, or only pushingthe mediastinum over towards the opposite side,or compressing the healthy lung. One fact indeedstands out most clearly, that is the amazingtolerance of the pleura and its resistance toaccidental infection.But when every allowance is made for enthusiastic

misapplication there is still no question thatartificial pneumothorax has added a new weaponto the treatment and control of tuberculosis andhas come to stay. What then are its uses ? Wholetext-books have been written in answer to this

question, and the Quarterly Cumulative IndexMedicus contains nearly 300 references to this

subject for the year 1932 alone. There appear tobe two broad views which influence the physician’sattitude : one school is impressed with the allergicresponse to a chronic infection treated on generallines, the other concentrates on the lesion in thelung. Dr. HEAF suggests that there has been atendency of late to invert the logical sequence ofthought. The question should not be-Can artificialpneumothorax be induced in this patient ? butrather Can this patient recover without any formof interference ? and the answer generally centresround that illusive conception " the early case,"and the value of a wait-and-see policy. But hereeconomic considerations may be paramount.Artificial pneumothorax may save the patientvaluable time and often long residence in a sana-torium, with consequent economy for the Statein bed accommodation. This attitude was putclearly from the point of view of the GermanState Insurance Scheme by Dr. GEORG KATZ,2who emphasised the social economies to be gainedfrom the earlier return to work and the reductionof sputum-positive cases. In this country Dr.H. BATTY SHAW has taken the same line, as maybe seen in a letter to our correspondence columnslast week. He has advocated immediate collapsetherapy, without a preliminary period of observa-tion, for the wage-earner-especially the indoorworker-the parents of young children, and thepoor, when the diagnosis of tuberculosis is con-firmed by bacteriological or X ray manifestationsor both. Dr. CEDRIC SHAW has made 3 a statistical

analysis of cases attending Dr. BATTY SHAW’Sclinic at the Brompton Hospital. His figurescontain a percentage of early cases which in otherhands would not have been subjected to lungcollapse, and he compares them with those ofMidhurst Sanatorium some years ago. The serieswas grouped, as in the Midhurst inquiry for theMedical Research Council by N. D. BARDSWELLand J. H. R. THOMPSON, into I., incipient ;II., moderately advanced; III., far advanced.There were in all 267 cases ; 184 went to a sana-torium after induction, 83 were treated by pneumo-thorax alone. The percentage mortality is almostthe same, whether they had sanatorium treatment

2 Die soziale und klinische Berechtigung zum künstlichenPneumothorax im Kampf gegen die Tuberkulose, Leipzig, 1929.

3 Quart. Jour. Med., April, 1933, p. 179.

or not, in groups 1. and III., but in group II. the" A.P.+sanatorium" class shows a slightly smallermortality. The aggregate rates of mortality in thetwo classes are very similar ; but when the sexesare separated, the rate for females treated by thecombined methods is lower than that for thosetreated by pneumothorax alone. As to the workingcapacity and the residual symptoms of the sur-

vivors, the differences between the two classes areinsignificant.

Of course the figures in the two series are toosmall to prove a superiority of artificial pneumo-thorax therapy over sanatorium treatment, but,clinical group for clinical group, the statisticaldifferences between the two have led Dr. CEDRICSHAW to conclude that active intervention holdsout a better prospect of restoring working capacitythan does sanatorium treatment, though this herecognises must remain a factor of importance fromthe educational point of view. He goes on to

suggest that if a case can be made out for thesuperiority of artificial pneumothorax over sana-torium therapy, then on humane, social, economic,and public health grounds artificial pneumothoraxin the individual patient should be undertakenearlier. In the past the grounds of opposition,he says, have been mainly two : (1) that the patientshould be allowed a " chance to beat the diseasehimself by a period of sanatorium treatment ;(2) that artificial pneumothorax exposes the

patient to a new and probably unnecessary setof dangers. These two objections, he considers,have been answered, in part or whole, by the figuresset out in his article. But even those who welcomethe statistical approach to this question can seethat there are a number of imponderable factorson both sides of the equation. With all its draw-backs-and they are many and obvious-thesanatorium has established itself in the treatmentof certain well-defined types of tuberculosis andany change of policy will need to be consideredlong and carefully.

SWIMMING BATH DANGERS

IT is a sound axiom that the first step towardssolving a problem is to define it correctly. It isalso wise, when an apparently satisfactory solutionhas been found, to go over the ground again andmake sure exactly what it is that we have dis-covered. This applies to practical affairs at leastas much as to the more theoretical aspects ofmedical science. A particular example is affordedby the practical problem of the disinfection of

swimming baths. This is an appropriate seasonto refer to some recent observations which suggestthat our routine methods of purification are

subject to important limitations.W. L. MALLMANN and W. CARY,’ working in

Detroit, U.S.A., have studied the results of chlorineand chloramine treatment of swimming-pool waterin relation to the utilisation of the pool by bathers.They point out that the routine method of testing,in which specimens of water are withdrawn at

1 Amer. Jour. Pub. Health, 1933, xxiii., 35.