Lewis Carroll, Alice in Wonderland

HARES HAVE enjoyed a mixed reputation over the centuries. In medieval times they were widely thought occasionally to turn into witches. Rather later, long before psychiatrists understood the importance of serotonin and noradrenaline levels as determining factors in the development of clinical depression, 18th-century doctors occasionally attributed the onset of acute melancholy to eating jugged hare.

This weekend, with the start of March, the hares will be dancing in the fields — just like Barry Flanagan’s sculpture of ecstatic dancing hares in the Waddington Galleries in Cork Street, or the hares in Alice in Wonderland. The hares currently leaping around the Norfolk marshes and fields are only mad with love, for this is the season of their mating. Their behaviour at this time of year has given rise to the term “as mad as a March hare” and has inspired the symbol of Luton Town football team. Luton was where felt hats were made, and hat-makers were driven to insanity — not by love but by repeated exposure to mercurous nitrate used in hat manufacture. Lewis Carroll wrote at different times of people being both as mad as a hatter, or mad as a March hare.

The poisonous nature of mercury has been recognised since the days of Hippocrates. He was the first doctor to write about the colic that it can cause, and Pliny wrote about its effect on the health of slaves who worked with this metal. In the past, chemists, laboratory technicians, dentists and farmers — who used mercury compounds for seed dressings — suffered outbreaks of mercury poisoning.

In 1953 the first account of poisoning by eating fish which had lived in water contaminated by mercury effluent, was reported from fishermen around Minamata Bay in Japan. In recent years mercury pollution of the sea and rivers and the subsequent contamination of fish has been a constant concern to public health physicians who are anxious about its potential effects. The greatest concern is for the unborn child and breast-fed babies — in both cases excessive quantities of mercury can damage the developing brain and central nervous system of the child.

In adult life patients who have absorbed mercury or inhaled mercury vapour lose their appetite, are emotionally unstable, sleepless, poorly co-ordinated and shaky, so that their handwriting makes that of the most dyspractic child look neat. As well as the tremor, they develop gastrointestinal symptoms, sore gums and dribble excessively. Older children become irritable and develop cold, pink and swollen extremities. When I started to practise it was not uncommon to see babies with so-called pink disease. This was mainly seen in babies or toddlers whose parents had given them a mercury-based laxative or a mercury ointment for nappy rash. Both remedies have been withdrawn.

Last week there was a new report from the Food Standards Agency, which advised pregnant women, and even women who intend to become pregnant, to cut swordfish, shark and marlin from their diet and to reduce their consumption of tuna to no more than two medium- sized tins or one tuna steak a week. This advice about tuna does not apply to older children or adults, but all infants and children under 16 are still advised to avoid eating shark, swordfish or marlin.

The problem with eating predatory fish is that when they devour smaller fish they concentrate the mercury derived from them in their own flesh. No harm will befall anyone eating the meat of stewed hare, but a swordfish steak may have levels of mercury five to seven times higher than is found in tinned tuna.

Tuna is particularly rich in the fish oils which are important for the optimum development of the developing foetus or baby’s nervous system, so that the withdrawal of such a ready source needs to be made up elsewhere. A survey in 1998 carried out by the then Ministry of Agriculture, Fisheries and Food revealed that herring and mackerel, and less oily fish such as cod and haddock, showed low levels of mercury which did not exceed a tolerable intake. There is a good case for drinking milk in which the formula includes additional long-chain polyunsaturated fatty acids (LCPs), better known to most people as omega 3 and omega 6 fatty acids.

Pregnancy tends to deplete a woman’s level of these essential fatty acids just when her developing baby’s nervous system is developing fast and it needs a high level. Breast-feeding also lowers a mother’s level of omega 3 and omega 6. Evidence has been growing that women who have low levels of LCPs tend to be more likely to have children who have smaller heads and a slower intellectual development. Likewise, some infants who do not receive enough omega 3 and omega 6 in early life do not develop a mature eyesight as quickly as their contemporaries. When older, it has been shown that these babies are not as fast at solving the problems that psychologists set for toddlers and small children.

In a well-nourished woman, breast milk should give the child enough of the LCP fatty acids, but in those who are not being breast-fed it is as well to use an artificial milk such as Milupa to which they have been added.

Women who doubt the quality of their nourishment might be advised to take additional fish oils to supplement their diet.

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