Tears contain a variety of different salts, most of which probably come from the blood and, ultimately, from the diet.
Salt in food is absorbed by the intestines and enters the bloodstream.
The salt probably enters tears as blood flows through the lachrymal glands, where tears are formed.
The first known chemical analysis of tears, published in 1791 in a scientific journal edited by the French chemist Lavoisier, noted that they contained sodium chloride, which is regular table salt, and other salts.
The second major salt in tears is potassium chloride, and there are also other things, like calcium, bicarbonate and manganese, that can be involved in salt formation.
Experiments in the 1950s showed that the concentration of sodium in the tears was the same as that in the plasma.
Salts are also excreted in urine and sweat.
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