Profitable Wonders
Salt, aka sodium chloride, is nowadays ubiquitous and so cheap that it’s easy to overlook how, from the dawn of civilisation onwards, it has been the most valued – and historically consequential – of commodities.
It has been determinant in the flourishing of great cities, the growth of trade, and the iniquities of slavery and colonialism; it’s been instrumental in the rise and fall of empires.
Salt’s pivotal role in human affairs reflects most obviously its supernatural ability to enhance the flavour and palatability of food. It not only has the piquancy of saltiness but influences for the better all the other taste modalities as well – balancing out sweetness, minimising bitterness and bringing out hidden aromas.
Nothing could taste flatter than unseasoned chicken stock, but add salt, notes chef and food writer Samin Nosrat, ‘and you start to detect complex and delightful flavours previously unavailable – the savouriness of the chicken itself, the richness of the chicken fat, the earthiness of the celery and thyme’.
Salt is also, of course, indispensable to life; just how indispensable the heroic physiologist Robert Mccance demonstrated in an experiment with himself as the subject. First he induced a state of salt depletion, sweating profusely for two hours while lying naked in a metal tunnel fitted internally with three rows of electric lamps.
For the next fortnight, he followed an exclusively salt-free diet, made more onerous by the tastelessness of his meals and a constant sense of nausea. He lost 13 pounds, becoming progressively weaker and more breathless, scarcely able to lift his arm to shave himself. Increasingly apathetic, he found that his mental processes slowed and ‘he longed for salt’.
His recovery at the end of this self-imposed ordeal was dramatic: within half an hour of eating a tablespoonful of salt, his sense of taste had returned; after
a few hours, his weakness and breathlessness had vanished. Two days later, he ‘jumped off the bus while it was still moving and could run upstairs’.
The debilitating consequences of Professor Mccance’s experiment can be accounted for, at least in part, by the role of salt (and sodium in particular) in propagating the electrical current along nerves and causing muscles to contract.
But more fundamental still (were that possible) is salt’s contribution to the constancy of the fluid ‘milieu interieur’ on which all of physiology depends, maintaining the integrity of the trillions of cells of the body, nourishing them with nutrients and hormones.
Put simply, this is how it works. Water is by far the largest constituent of the body – 42 litres (or 72 pints) in total. That subdivides into two main compartments: two-thirds (27 litres) being intracellular – ie within those trillions of cells – and the remaining third (14 litres) being extracellular – ie on the outside – bathing the cells with those essential nutrients and hormones.
The constancy of those amounts of fluid in these two compartments is paramount: too much water within the cells and they become waterlogged; too little outside and the tissues become dehydrated. The seemingly insurmountable difficulty in maintaining that constancy lies in the fact that each of those trillions of cell also contains all the complex structures necessary for fulfilling its diverse functions. The nucleus contains all those genes strung out along the double helix, the machinery for making the thousands of different types of proteins, the energy-generating mitochondria and so on.
The presence of all these structures within the cell should by rights markedly increase its osmotic pressure relative to that of the extracellular fluid. This should, in turn, initiate the universal phenomenon of osmosis, with water moving across the cell wall from the extracellular compartment into its interior to equilibrate those pressures – but that would cause the cell to swell inordinately till its soap-like bubble of a membrane ruptured.
To prevent this from happening, the cell pumps all the salt (or the sodium and chloride ions) outwards till its concentration is ten times greater in that extracellular compartment. That precisely neutralises the osmolar effects of those vital structures (the nucleus, mitochondria etc), reducing the pressure difference to zero and thus maintaining the constancy of the amounts of fluid in the two compartments.
Life is full of miracles – but none quite as miraculous as this.