805

the amount of clinical material on which the student canbe taught is diminishing, partly as a result of the increasingsuccess of conservative dentistry and improved oral

hygiene, and partly because of the wide usefulness oflignocaine as a local anxsthetic. So much indeed has thenumber of cases for general anxsthesia been reduced thatto find enough cases for postgraduates is becomingincreasingly difficult. This is a major problem, since

provision for postgraduate teaching is essential. Perhapsmaterial in local-authority clinics could be used to supple-ment that in teaching centres, though the bulk of thepatients are children and in some areas the number ofpatients presenting themselves for extraction under

general anaesthesia has been reduced by 25 % in the pastfew years.There is no difficulty in providing postgraduate lecture

courses in anaesthesia, and it is noteworthy how enthu-siastic dentists are to attend these. Perhaps a diploma indental anxsthesia might be instituted for those devoting,say, six months of more or less continuous postgraduatestudy to the subject. A diploma must, if it is to be of value,indicate that its holder is proficient, not merely in theordinary dental gas, but in the use of intravenous agents,volatile supplements, relaxants, and endotracheal intuba-tion. For medically qualified anaesthetists it would berather difficult to justify the introduction of such a

qualification, since the holder of the existing diploma inanxsthetics must have the basic knowledge required fordental anxsthesia, though his practical proficiency willdepend on the extent of his experience in this field.

DRUGS AND BEHAVIOUR

PSYCHOLOGICALLY oriented experiments on drugs andbehaviour are important not only for the essential clinicalinformation they give but also for the clues they supplyabout the organisation of the central nervous system.Tranquillisers, depressants, and hallucinogens are of

special interest. The information that these experimentsmay uncover relates to motor accuracy, coordination and

speed, decision-making (such as a correct response to achoice of signals), impairment of mental processes, andshort and long memory. The conditions of experimentmust be carefully controlled, for experience and repetitioncan alter results.

Barbiturates and amphetamine are among the drugsthat have been used in these experiments; and some recentdevelopments are discussed in the British Medical Bulle-tin.1 Barbiturates impaired performance in all tasks; andamphetamine improved arithmetic but not certain move-ments requiring accuracy. When the two were giventogether, the amphetamine counteracted the barbituratedespite its own lack of significant effect; but the bar-biturate did not counteract the tachycardia produced byamphetamine.

Studies have also been made of chemically similar anddissimilar drugs, and their effects can be compared withknown pathological states. In this way the anatomicalregion or control system affected by the drug can to someextent be deduced, and it may be possible to decide’ hether any of the effects are partly or wholly peripheral.An ingenious technique has been used to gain knowledgeof the processes involved in memory formation andretention. A very quick-acting and short-lasting drugnitrous oxide was given in subansesthetic doses at

1. Summerfield, A. Brit. med. Bull. 1964, 20, 70.

chosen times after the learning process, and the effect ofthe interruption on learning and memory examined. Theconclusion was that forgetfulness was probably due tointerference before the learned process could be firmlyimplanted. It became clear in all experiments of any kindthat basic personality affected the response to drugs; buteven when personalities seemed similar, variability of

response might be considerable.Hypotheses regarding the mode of action of drugs in

man can be tested by studying behavioural responses inanimals given the drug.2 Thus, one of the major effects ofamylobarbitone was supposedly to reduce fear, and thisaction was examined in rats. The animals were first taughtto obtain food and water by pressing levers; and they werethen examined during drug treatment and when a mildelectric shock was interposed between them and the food.The results suggested that " fear " was in fact reduced,and this impression was corroborated by other observa-tions. It became evident that the drug did not interferewith the process of learning, so that a double end wasachieved by these experiments.

Animals may be given tranquillisers in an attempt tofind antagonists which can then be tried on patients withdepressive illnesses. Again, the effects of combinationsof drugs can be examined to see whether they potentiateor antagonise each other. In animals, too, it is easier tocompare the effect of drugs with that of lesions of thecentral nervous system; thus, important differences werefound between the effect of reserpine and lesions in theamygdala, where it had been thought that the drug mighthave its action. In animals, as in man, personality affectsdrug response. As more work is done, so the skill increaseswith which useful and appropriate behaviour tests can bechosen and applied.

TANNIC ACID IN BARIUM ENEMAS

MANY radiologists favour a barium enema containingtannic acid, which improves the quality of the pictures.But the safety of this practice is now in question. OnMarch 21 the United States Food and Drug Administra-tion gave notice of their intention to withdraw approvalof ’ Clysodrast’, a combination of tannic acid and alaxative [4,4’-(diacetoxydiphenyl)-(pyridyl-2)-methane,’

Dulcolax ’] used before radiological examination of thelower bowel. The F.D.A. state: "Cumulative clinical

experience shows that the use of ’ Clysodrast ’, and thatthe use of tannic acid, a component of ’ Clysodrast ’, byrectal administration as an enema has been associated witha number of deaths involving necrosis of the liver, andthere is no available adequate evidence of toxicity studiesin animals and liver-function studies in man showing thelevels of safe use of tannic acid alone or in combinationwith other components of ’ Clysodrast’ when used as anenema in preparation for a barium enema."

Tannic acid can damage the liver; and when it waswidely used in the treatment of burns it was not appliedto large areas of burned skin because it might be absorbedin sufficient quantity to affect the liver.We have not yet had full details of the evidence on

which the F.D.A. action is based; but the matter mustclearly be treated very seriously. In this country the

Ministry of Health is ensuring that radiologists are

informed of the situation; and the Dunlop Committee onSafety of Drugs will be studying the available facts.

2. Steinberg, A. H. ibid. p. 75.