In the 16th century the Swiss philosopher Paracelus, promoted the use of three symbols to represent what he called the three primes. These were 3 elements believed to be responsible for all diseases and poisons in the human body and by studying them that alchemists could work out how to cure diseases. The Three Primes were also thought to represent the soul, spirit and the body and that when two of them were put together they would produce the third. For example the masculine element of Sulphur when combined with the opposing feminine element of Mercury this would create the third element of the primes, Salt.
Paracelus was a 16th century Swiss philosopher who devised the theory of the three prime elements and linked them to human diseases.