In this pilot study, remifentanil by PCA gave better pain relief to mothers in labour than intramuscular meperidine. However, remifentanil is a potent respiratory depressant and adequate continuous monitoring is necessary.

In 1945 we reported (Dick & Bull, 1945) the first observations on the effects of molybdenum in the diet of ruminants in limiting the accumulation of copper in their tissues.Further observations (Dick, 1952) indicated that there was a third factor which materially altered the control by molybdenum of copper accumulation and this factor, present in lucerne hay, was identified as inorganic sulphate (Dick, 1953a). It was also shown that sulphate regulated molybdenum excretion (Dick, 1953b) in the urine and hence the level of molybdenum in circulating blood (Dick, 1953c).

Experiments reported in this paper show that increased copper intake of sheep is reflected by increased copper content of the liver. The magnitude of the rise in liver copper depends upon a number of factors, but under the described conditions, the amount of copper accumulated by the animal is proportional to the copper intake within the range 3-20 mg per day; the amount stored in the liver over a 6 months1 period was found to be 4.5-5 per cent. of the intake. Some of the conditions which may modify the retention of copper were examined. It was found that the addition of ferrous sulphide to the diet, which presumably converts added copper to the insoluble sulphide, lowered the expected copper accumulation in the liver by 75 per cent. Conditions which may modify this effect of ferrous sulphide have been examined and described. Other possible sources of sulphur for the formation of copper sulphide in the animal (elemental sulphur, sodium thiosulphate) were found not to be effective. The effects of some other metals (zinc, nickel, iron, and molybdenum) on copper accumulation in the liver were examined. Molybdenum was found to have a severely limiting effect, but this effect was only observed when the diet also contained a sufficient quantity of inorganic sulphate. For a given intake of molybdenum the limitation of copper storage was found to be proportional to the sulphate content of the diet. The possible bearing of these experimental findings on conflicting field observations relating to copper metabolism of sheep is discussed.

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