421

some other container for dipping and a third container usedfor transmission to the laboratory (few wide-mouthed con-tainers are watertight). This difficulty leads me to preferthe Mackey spoon.The plastic Mackey spoons used to be resistant to heat

and capable of re-use. It seems that because of this it wasnot profitable to make them and now only polyethylenespoons, which melt when heated, can be obtained. Thismakes the Mackey-spoon technique more expensive than itused to be, but it is still much cheaper than uricult slides.The spade-shaped dip-spoon recently devised by OxoidLtd. is likely to be as good as the Mackey spoon, but if a" good " MacConkey medium is made there is no need touse two different media on the same dip-spoon or slide.

M. H. HUGHES.

Public Health Laboratory,Royal Hampshire County Hospital,

Winchester.

SWALLOWED NEONATAL ENDOTRACHEAL

TUBE

ARON STORCH.

Department of Obstetrics and Gynecology,Kaiser Foundation Hospital,San Francisco, California.

SIR,-With reference to the article by Dr. Abrahams andhis colleagues (July 18, p. 135) may I refer you to an articlein the July, 1970, issue of the Journal of Pediatrics (p. 123) ?In this, Dr. G. C. Calderwood and I suggested the attach-ment of a silk suture, or any other nonabsorbable type ofsuture, to the end of the endotracheal tube. This preventsany problem arising if the tube is swallowed, since thesuture allows easy removal. The suture, inserted in thehorizontal plane to prevent kinking of the tube, does notinterfere with any attachment to the tube.

Obviously the redesigned tube, possibly with an exten-sion of the initial tube, would be preferable even to thismethod.

PLASMA-CATECHOLAMINE ESTIMATIONS

SIR,-We would like to point out that our article on thevalidity of plasma-catecholamine estimations was in noway intended to detract from the method of McCullough,2as might be inferred from the letter of Miss Davis andMr. Sheridan (Aug. 15, p. 364), but rather to add to it.For example, we found that both the sensitivity andreproducibility of the method could be considerablyimproved by certain modifications, particularly by stabilisingthe temperature of the final fluorescent mixture, of whichthe original McCullough method makes no mention. It iswell recognised 3 that failure to do this, especially at lowconcentrations of catecholamines, may cause variations ofup to 14° per degree centigrade change in temperature.The common occurrence of variation in laboratory tempera-ture of up to 10°C has been regarded as invalidating allmethods where this has not been taken into account.3 3

Further, the McCullough method only states that theblood-sample should be chilled in ice for an unspecifiedperiod, until centrifuged. In our experience this mayresult in considerable losses, as may be seen in tables IVand v of our article. Their point about the presence ofcatechol-o-methyl transferase in red blood-cells, we our-selves endeavoured to illustrate in fig. 3. Our work also

suggests that each of the wide range of amine oxidases inblood is likely to be highly substrate-specific, which makesit difficult to ensure their absence from any particularfraction.

1. Carruthers, M., Taggart, P., Conway, N., Bates, D., Somerville, W.Lancet, July 11, 1970, p. 62.

2. McCullough, H. J. clin. Path. 1968, 21, 759.3. Gerst, E. C., Steinsland, O. S., Walcott, W. W. Clin. Chem. 1966,

12, 659.

As we note under " the effect of prolonged storage ",pH can influence the rate of decay of catecholamines.However, experiments on deproteinised plasma indicatethat blood pH is unlikely to be the factor responsible forthe in-vitro decay which we have demonstrated.We hope that the points we made will prove helpful

to other investigators and narrow the scope for potentialerror, so that this useful method of investigation will notfall into disreoute.

MALCOLM CARRUTHERSPETER TAGGARTWALTER SOMERVILLE.

Courtauld Institute of Biochemistry andDepartment of Cardiology,

Middlesex Hospital,London W.1, and

Institute of Ophthalmology,London W.C.1.

GLUCAGON AND THE HEART

ROBERT ROSENBLUM.

Cardiology ServiceDepartment of Medicine,

Montefiore Hospital,Bronx, N.Y. 10467.

SiR,-Your excellent editorial on glucagon (July 18,p. 137) requires further comment. You quote the results ofGlick 1 comparing the effects of glucagon, noradrenaline, iso-prenaline, and dopamine on renal blood-flow; but these arebased on an unphysiological experimental design. Nor-

adrenaline, isoprenaline, and dopamine are rarely if everused clinically or experimentally by single-bolus injection,as they were in this investigation. In addition, the con-centration of dopamine used is known to produce peripheraland renal vasoconstriction. In physiological doses byconstant infusion, dopamine decreases renal resistance aswell as increasing cardiac output.2,3

COXSACKIE MYOCARDITIS

OF THE NEWBORN

P. V. SUCKLINGL. VOGELPOEL.

Cape Town,South Africa.

SIR,-In 1958,4 we reported on 8 cases of Coxsackie-B,myocarditis in newborn children. 4 lived, and we havetraced 3 of them, now aged 13 years. Prof. V. Schrire, ofthe cardiology department, University of Cape Town, haslately examined them and reports that they are clinically,radiologically, and electrocardiographically normal.

COMPARISON OF ANTIHYPERTENSIVE AGENTS

AUSTIN T. CARTY.Mater Hospital,Dublin 7.

SIR,-I must take issue with Dr. liibb and his colleagues(Aug. 8, p. 275) for the levity with which they dismiss thecontribution of thiazide in the reduction of blood-pressureof the patients in whom they compared bethanidine,tx-methyldopa, and reserpine. The level of untreated

pressure of their patients was not remarkably high (meandiastolic pressure about 116 mm. Hg). The dose of thiazideused was substantial, but, as might have been expected, thedoses of trial drugs which had to be added to the thiazidewere small. There is no evidence that the reduction in

blood-pressure achieved in their patients could not beattributed in great part to the thiazide, and that the con-tribution of the trial drugs in the doses in which they wereused was not trivial and incidental. Without a control grouptreated with thiazide alone I fear that no meaningful con-clusions about the relative merits of bethanidine, oc-methvl-dopa, and resernine can be drawn from their work.

1. Glick, G. Clin. Res. 1970, 18, 307.2. McDonald, R. H., Jr., Goldberg, L. I., McNay, J. L., et al. J. clin.

invest. 1964, 43, 1116.3. Rosenblum, R., et al. Clin. Res. 1970, 18, 326.4. Suckling, P. V., Vogelpoel, L. Med. Proc. 1958, 4, 372.