The Line of Mercury, or of Health, relating as it does to the nervous system, and also to the mind (Mercury), lends itself to the supposition that the all-knowing subconscious brain is cognisant, even at an early age, of the force of resistance in the nervous system. It may know how long this force will last, when it will be exhausted, and consequently may mark the hand long years in advance.
The Line of Health is one of the lines of the hand most subject to changes. It is the thermometer of the life showing its "rise and fall" as the case may be. I have seen this mysterious line look deep and threatening during the early years of a life, and completely fade away as greater health and strength took possession of the body.
Again, I have often seen it look deeper and more ominous as the wear and tear, especially of the nervous system, began to make itself manifest, or when the subject over-taxed his mental strength.
Further, it is an excellent sign to be without this line altogether. Its absence denotes an extremely robust, strong constitution, and a healthy state of the nervous system.
If a hand has the Line of Health, the best position for it is to lie straight down the hand, and not approach or touch the Line of Life (3-3, [Plate XIX].). When found crossing the hand, and touching or throwing branches across to the Line of Life, it foretells that there is some illness at work which is undermining the health.
If it rises and seems like a branch from the Heart Line, especially if both these lines are broad in appearance and with the Health Line running down the palm coming in contact with the Line of Life, it is a certain indication of weakness or disease of the heart.
The student should always observe the kind of nails there are on the hand when thinking out the diseases indicated by the Line of Health.[6]