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spend a considerable proportion of their time in the com-munity following up this type of patient. The readmissionfigures are given in the paper.The patient mentioned by Dr. Shepherd was diagnosed

as suffering from subnormality at the Maudsley. He wasadmitted and discharged from St. Mary Abbots in 1967(this was the year I reported in the paper). He was re-admitted in 1968 and during his stay was seen by a consul-tant from Leavesden Hospital who agreed the diagnosis ofsubnormality and accepted him for Leavesden.

Dr. Barker and Dr. Bewley raise another important point.My colleagues and I admit to St. Mary Abbots all thefunctional psychiatric conditions in old age and those

psychogeriatric patients where there is clearly a need forcare under a psychiatrist and psychiatric nurse, as opposedto geriatric care. From the point of view of future planning,it is important that one part of the medical service shouldnot be used to subsidise another part. We should plan fora comprehensive psychiatric service and equally geriatri-cians will wish to plan for a comprehensive geriatric service.

I think that there will be a small number of long-staypatients coming from psychiatric units in district generalhospitals. These patients, however, are likely to have

multiple handicaps, both physical and mental, and are

patients who will need the resources of the district generalhospital, though perhaps their needs will be better served inthat part devoted to the younger chronic sick.

I have no doubt that a unit such as St. Mary Abbots canprovide a better service for psychiatric patients, whetherthey be acute or long-term, than can the old type of mentalhospital. I agree, however, with the correspondents whopoint out the need to assess the results in detail, and hopethat resources will be made available to make this possible.

A. A. BAKER.St. Mary Abbots Hospital,

London W.8.

SHOULD DIABETICS MARRY ?

SIR,-We would like to associate ourselves whole-

heartedly with Professor Edwards 1 who has consistentlypointed out that familial aggregations do not necessarilyindicate a genetic defect, especially since no chromosomalabberrations have as yet been noted in diabetes mellitus.There is abundant published evidence that the mode ofinheritance of diabetes is not clearly established. Vallance-Owen 2 regards it as an autosomal dominant, Penrose andWatson 3 as sex-linked, Pincus and White 4 as recessive,and Simpson 5 as multifactorial.

In a recent study of 350 diabetic children under the ageof 16 we found that 95% of the parents were not diabetic.50% of the families had a relative with diabetes and theseranged from great-aunts and great-uncles to second cousins,many of whom were over 40 years old and a considerablenumber of whom were treated by diet alone. We were alsoimpressed by the fact that 12 children had a precedinghistory of chickenpox three weeks before the onset offull-blown diabetes mellitus.John 6 has long suggested that diabetes may be caused by

infection. Mumps has been accepted as producing diabetes.Recently, Craighead et al. showed that encephalomyeliticstrains of virus produced diabetes in mice treated with thevirus. Clearly, there are some cases of diabetes that are notinherited. Therefore to condemn diabetics to a life ofpurgatory because of the fear of the consequences of having1. Edwards J. H. Lancet, 1969, i, 1045.2. Vallance-Owen, J. Diabetes, 1964, 13, 241.3. Penrose, L. S., Watson, E. M. Proc. Am. Diabetes Ass. 1946, 5, 165.4. Pincus, G., White, P. Am. J. med. Sci. 1933, 186, 1.5. Simpson, N. E. Ann. hum. Genet. 1962, 26, 1.6. John, H. J. J. Pediatrics, 1949, 35, 723.7. Craighead, J. E., McLane, M. F., Steinke, J. Metabolism, 1968,

17, 1154.

diabetic offspring, in the absence of any accurate probabilitytable, is unrealistic and turns the scientific doctor into amystic.With the increased sensitivity of tests for carbohydrate

intolerance, the number of elderly diabetics will increaseand every family will have at least one diabetic relative if therelatives live long enough. It might be as well for the WorldHealth Organisation to put the question: " Should anybodymarry ? "

NAOMI BAUMSLAGRALPH E. YODAIKEN.

Departments of Environmental Healthand Pathology,

U.C. Medical Center,Cincinnati, Ohio.

CARPAL-TUNNEL SYNDROME

SIR,-We should like to answer some of the points madein the correspondence which arose from our article on thecarpal-tunnel syndrome (May 3, p. 918). Dr. Backhouse andDr. Kay (June 7, p. 1150) question the lack of prominencegiven to rheumatoid arthritis in our report. We would notdeny the frequency of median-nerve compression in arheumatoid population, which has been demonstrated byvarious workers, but our series was drawn from patients withdistal sensory symptoms in the upper limbs referred to

general orthopxdic clinics. Of our 113 patienrs only 1 hadclinical evidence of rheumatoid arthritis. Our impression,from the Oxford medical-record-linkage study, is that thelarge majority of patients undergoing operative carpal-tunnel decompression in our region do not have rheumatoidarthritis.As Dr. de Swiet pointed out (June 7, p. 1151) we did

indeed omit to mention that myxoedema is an indication forconservative treatment.

Dr. Matricali and his colleagues (June 14, p. 1217) rein-force our advocacy of preoperative electrodiagnostic con-firmation of median-nerve compression; but this facility isnot as widely available as one would wish. We still believethat clinical suspicion is a reasonable indication for opera-tion, though prognosis should be more guarded than it wasin the past.

J. C. SEMPLEA. O. CARGILL.

Nuffield Orthopædic CentreHeadington,

Oxford OX3 7LD.

BLOOD GASES AND LUNG FUNCTION

SIR,-Dr. Fairley 1 suggests that the regression equationswe gave for patients with chronic obstructive bronchitisfor predicting probable values for arterial oxygen tension(Pao2) and carbon-dioxide tension (Paco2) from a knowledgeof the F.E.V.1 (May 31, p. 1073) may, in spite of highlysignificant correlation coefficients, give misleading informa-tion because the standard errors are large. This is a

common problem when regression equations are derivedfrom clinical data. We acknowledge the statistical validityof his comments but think that in a clinical situation the

equations can nevertheless in the majority of instances giveguidance to the probable blood-gas tensions, and we do notclaim more than this.We agree that changes in arterial oxygen tension are not

related in a linear fashion to oxygen content, and it may be,as he suggests, that the relationship between lung functionand arterial oxygen content might be more meaningfulclinically. We have no information on this point at themoment.

A correlation between Pao2 and single-breath carbon-monoxide transfer factor (D.L.CO) was not given because,although Pao2 fell with increasing airway obstruction,D.L.CO remained at a low but constant level irrespective

1. Fairley, H. B. Lancet, 1969, i, 1313.