its discharging it self thro' proper Ducts, at certain Intervals, when the pressure of the external Air being diminish'd, the internal Aura can exert its Elasticity; so in the other, if at any time there happens to be a Superabundancy of the same Fluid, together with a weak Tone of the Fibres; it is plain that the Vessels will be most easily burst, when the Resistance of the Atmosphere is least. And this more especially, if any accidental hurt, or rarefying Force has first given occasion to the other Causes to take effect.
I know a Gentleman of a tender frame of Body, who having once, by over reaching, strained the parts about the Breast; fell thereupon into a spitting of Blood, which for a Year and half constantly return'd every New Moon, and decreasing gradually, continued always 4 or 5 days. The Fits being more or less considerable, according as his management about that time, contributed to a greater or lesser fullness of the Vessels.
We have two notable Instances of the like nature in our Philosophical Transactions; the one[33] of a Person, who from his Infancy to the 24th Year of his Age, had every full Moon an Eruption of Blood on the right side of the Nail