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and irrational factors underlying the behaviour of students(and their tutors) and must have a continuing concernwith the impact and meaning of the pressures anddemands made by the university upon the student. In

practice, the college doctors in the proposed Oxfordscheme will need further training in these skills, and thisis probably best achieved in the mutually supportiveatmosphere of seminars supervised by psychiatrists-orin a student health teaching unit, as envisaged in theRoyal College of Physicians’ report.14 The universitymedical officer will need a brief which includes, as wellas the organisation of the service and the provision ofsome clinical treatment, work with tutors and researchinto the broad health implications of the various aspectsof the academic and social life of the university. Drug-taking by students would surely be one problem withinthe sphere of this new university medical officer.

It is therefore surprising to find that the committeeproposes to make this "key figure"-the university medicalofficer-a part-time appointment, with, apparently, noacademic status. To combat the occupational risk of over9000 undergraduates, plus graduates and possibly someteaching staff, with such half-hearted generalship couldbe a fatal flaw in the scheme. In trying to placate theproudly or obstinately autonomous colleges, the com-mittee may have compromised the whole scheme.

RENAL STONES AND SODIUM

WHEN the treatment of a disease is reasonably clearcutand effective, the urge to discover the underlying causeis less obsessive than when treatment is haphazard andthe physician must work by rule-of-thumb. There arewell-endowed institutes, foundations, and centres for

investigating cancer, heart-disease, and rheumatoid

arthritis, but none for appendicitis. Who cares about thecause of appendicitis ? Remove the diseased appendix,and all is well. Again, with stones in the kidney, treat-ment on the whole nowadays leaves little room for

deviation, and the result is generally successful-but westill do not know why some people and some animalsform stones in their kidneys.This disease displays regional and racial variations; and,

basing his views on the well-documented finding thatrenal stones are almost unknown in the Bantu of southernAfrica (in contrast with white inhabitants), Modlin 15 givesan attractive hypothesis to account for the difference. Hebegan by examining 24-hourly collections of urine froma group of stone-free white men, a group of Bantu men,and a group of white male patients who had formedstones (men only, because men are more liable to formstones than women). Modlin’s findings led him to rejectolder views that the absolute daily urinary levels of totalcalcium, ionised calcium, citric acid, phosphate, and

magnesium, or the concentration or proportion of urinaryionised calcium were relevant to the genesis of stones.Neuman and Neuman 16 suggested that a crystalline struc-ture resembling that of hydroxy apatite could induce theaggregation of calcium and phosphate ions. For this to

happen, two crystal faces in contact must have a like

crystalline lattice. On this reasoning, stones form by theintergrowth of crystals-a process of seeding, therefore,rather than of precipitation, which Royer 17 had named

15. Modlin, M. Ann. R. Coll. Surg. 1967, 40, 155.16. Neuman, W. F., Neuman, M. W. Chem. Rev. 1953, 53, 1.17. Royer, L. Bull. Soc. fr. Minér. Cristallogr. 1928, 51, 7.

epitaxy. Modlin suggests that the lattice structure of

mucoproteins or other crystals in urine resembles that ofhydroxy apatite. Hence, in suitable circumstances and inthis way, renal stones begin to form.

But what causes stones to form in the white people ofSouth Africa in the same proportion of the population asin Europe and yet leaves the Bantu relatively unscathed ?For that matter, why should some but not all white

people have renal stones ? The answer, Modlin believes,must lie in the presence in normal urine of an inhibitorof crystallisation. He found that the urinary output ofsodium in the Bantu was strikingly high. The mean24-hour urinary sodium was significantly higher in theBantu, and it was significantly higher in the white controlswithout stones than in the white group with stones.

Laboratory evidence points to sodium as an inhibitor ofcalcification; and Udall and Fu Ho,18 who added salt tothe diet of 48 lambs before slaughter, found that nonehad detectable stones, but that 29 out of 48 lambs. not

given extra salt had formed stones. This seeming capacityof sodium to increase the solubility of calcium in theurine was attributed by Neuman and Neuman 19 to thecompetitive binding of sodium and calcium ions to

crystals of hydroxy apatite. By displacing calcium ionsin solution (and even in the solid state), sodium increasesthe solubility of hydroxy apatite or the correspondingtype of urinary crystal. This increase in solubility is afunction of the concentration of sodium relative to calciumin solution. Turning again to 24-hour urine collections,Modlin found that the mean daily urinary sodium/calciumratio was significantly higher in the Bantu than in thewhite controls, and significantly higher in the white groupwithout stones than in the stone cases. He concludedthat liability to form renal stones decreases with anincrease of the amount of sodium relative to calcium inthe urine.

Unlike urinary calcium, urinary sodium is directlyrelated to the dietary intake. Average salt intake inWestern communities is of the order of 10 g. per day; inthe Bantu it reaches 17 g.-a dietary peculiarity of theBantu, who are given to excessive seasoning of their foodwith salt. Their freedom from renal stones is presumablydue to their high intake of salt, with a consequent highsodium/calcium ratio in the urine. By the competitivesubstitution of lattice ions, calcium is displaced, and thenucleus of a potential stone is dissolved.

In support of this hypothesis, Modlin cites the findingsof Japanese workers and estimations derived from anEskimo population which seem to confirm that the averagelevels of salt intake in a particular region are inverselyrelated to the prevalence of renal stones. Eskimos, in fact,have a low daily average intake of salt: here the relativefreedom of Eskimos from renal stones is accountedfor by their surprisingly low urinary output of calcium.As in the Bantu, therefore, the sodium/calcium ratiois high. In the same way, the familial tendency to

form renal stones, noted by some observers, may berelated to conformity in the consumption of salt amongfamilies.

Modlin acknowledges that his conclusions are tentative.Nevertheless, even if the findings do not call for theestablishment of a special centre or an institute, interestedworkers must test his hypothesis.18. Udall, R. V., Fu Ho, C. C. Ann. N.Y. Acad. Sci. 1963, 104, 612.19. Neuman, W. F., Neuman, M. W. in The Chemical Dynamics of Bone

Mineral; p. 169. Chicago, 1958.