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the isolated rat tail artery, we tried to correlate step levels ofintravascular pressure with ionic transfers in the vascular wall,as measured by means of Na+ and K+ sensitive electrodes. K+efflux from and Na+ influx into the vascular cells in responseto changes in transmembrane distending pressure were clearlydemonstrated. A direct close correlation was noted between

changes in perfusion pressure and ionic shifts. The effect ofthe distending pressure was most readily explained by a tran-sient increase in the permeability of the smooth-muscle cellmembrane, associated with increased myogenic activity, dur-ing which K+ and Na+ moved out and into the cell along theirrespective downhill concentration gradients.

These findings on smooth-muscle cells accord with Garayand Meyer’s hypothesis that primary changes in the trans-membrane concentration gradients of Na+ and K+ could be re-sponsible for an increased vascular contractility in patientswith essential hypertension.Service de Pédlatrie,Centre Hospitalier Universitaire Vaudois,1011 Lausanne, Switzerland JEAN-PIERRE GUIGNARD

NIGHT COUGH IN CHILDREN

SIR,-I am not known for any overenthusiasm for what isunderstandably sometimes called ritual dissection of the lym-phoid tissue of the nose and throat, but I agree with Dr Wind(Feb. 17, p. 382) that enlarged adenoids are an occasionalcause of night cough in children. Perhaps the E.N.T. surgeonsapproached by Hibbert’ did not mention this as an indicationfor adenoidectomy as they were contacted by telephone with alist of direct questions, of which this was not one. I doubtwhether the cough is a direct result of irritation from theadenoids themselves and my own theory is that chronic mouthbreathing results in drying of the tracheal and bronchialmucosa lowering the level at which the cough reflex can be eli-cited and delaying recovery from viral lower-respiratory-tractinfections. I was very interested in Wind’s reference to cough-ing resulting from stimulation of nasal, pharyngeal, and laryn-geal receptors and would like to know what his evidence forthis is. I personally do not believe that the cough reflex can beelicited in the upper respiratory tract and that coughing is evercaused by enlarged tonsils, pharyngitis or post-nasal drip2-’ (anunlovely, unscientific, and misleading term that should bebanned). -

There are few indications for adenoidectomy but it would bea pity if those children who clearly benefit from the simpleand, these days, painless, and uncomplicated prophylactic pro-cedure should be condemned to protracted ill-health and medi-cation unnecessarily.York District Hospital,York YO3 7HE CHARLES SMITH

MEMORY

StR,—You reviewed some interesting experimental work inanimals (Feb. 24, p. 418) but I am doubtful how far its directapplication to memory in man is justified. Memory is used indifferent senses and you seem to have transposed a biologicalmeaning-retention of acquired behaviour-to a clinical set-ting where usage implies voluntary recall or recognition of pastexperience. Gibbs5 was working with day-old chicks and study-ing the retention of a learned avoidance reaction. In that set-ting he suggested that three memory systems rather than two(as at present widely accepted for human memory) were in-volved. Oakley and Russell found that conditioning of a nicti-

1. Hibbert, J. Clin. Otolar. 1977, 2, 239.2. Pheland, P. D. Lancet, 1978, ii, 1309.3. Stell, P. M. ibid. March, 17, 1979, p. 616.4. Lancet, 1978, ii, 773.5. Gibbs, M. New Scientist, 1979, 81, 261.6. Oakley, D. A., Russell, I. S. Physiol. Behav. 1977, 18, 931.

tating membrane response was still possible in neo-decorticatewhite rabbits--evidence that the neo-cortex is not essential forthe formation of memory in this sense. Neither of these find-ings seem at present very relevant to memory in man.

de Wied’ has shown that in the white rat the extinction ofa learned avoidance response can be delayed by vasopressin,and that it appears to act on the consolidation rather than theinitial learning process. He clearly states his biological defini-tion. However, with the emotional demand for an elixir of

memory, this work has already led to trials of vasopressin inKorsakoff and traumatic amnesia, with conflicting results.Before larger and better controlled clinical trials are under-taken, it would seem logical to confirm these observations insub-human primates, where complexity of cerebral structureand function may be more akin to that in man, and where

sophistication of behaviour allows assessment of somethingnearer to memory as defined in clinical work. It might also bemore informative to mount such trials in patients with cir-cumscribed memory defects and cerebral lesions, rather thanin those with the additional "dementia" and more widespreadpathology of Alzheimer.

Department of Neurology,Radcliffe Infirmary,Oxford C. W. M. WHITTY

BABIES WHO BREAST-FEED AND FAIL TO THRIVE

SIR,-May 1 respond to the invitation in Dr Davies’ paper(March 10, p. 541) by recording some points based on mysupervision of breast-feeding both in postnatal wards and in abreast-feeding clinic. I can confirm that there has been an in-crease in failure-to-thrive babies due to underfeeding on thebreast. The "contented" underfed breast-fed baby is the

greater problem since it is easily overlooked both by themother and sometimes the child-health clinic. It tends to pres-ent later than the fretful underfed breast-fed baby-i.e., at4-6 weeks, often at or below birth weight and in an emaciatedcondition. Do these babies have a defect in appetite control,which diminishes stimulation of the breast by inadequate suc-king ?The contented underfed baby seems to suck well, but can be

seen to swallow little milk, and test weighing shows it to havea grossly inadequate intake. I agree with Davies that it is un-likely that a mother whose baby is admitted to hospital for fail-ure to thrive due to insufficient milk can establish successful

breast-feeding.Truly demand breast-fed babies lose little weight in the first

4 days and often regain their birth-weight by the 7th day.Health visitors should be alerted by any baby passing into theircare with a discrepancy between birth-weight and dischargeweight. Notification to the health visitor by the maternity hos-pital or district midwife requesting an early visit would help inthe detection of underfeeding problems at a stage when it isstill possible to improve the mother’s lactation by more fre-quent feeding and supervision.An assessment at a breast-feeding clinic a few days after dis-

charge from hospital will usually show whether breast-feedingis going to be sufficient without any complement and whethera mother can be safely left to continue breast-feeding super-vised by the health visitor at home. Those with minor degreesof insufficiency and a fretful baby will often improve; othersmay complement feed; some will successfully breast and bottlefeed, and maintain their milk supply providing that they offerthe breast first for 5-10 min a side.The prevalent idea that if a mother breast-feeds her baby

often enough and for long enough at each feed that she willbe sure to produce enough milk is fallacious if applied to allstages of lactation: a "fretful" underfed breast-fed baby andan exhausted mother may be the result of such a policy. An7. de Wied, D. Nature, 1971, 232, 58.