10. Lastly, to form some idea of the nature of contagion, or infection, as it is more properly called, we must consider, that as the ethereal fluid, acting as heat, pervades the human body, so doth it likewise under that particular modification which we call electricity. Some kinds of air, indeed most of those with which we are acquainted, seem to act by augmenting or diminishing the latent or the sensible heat of the body. Such, when taken in moderate quantity, may produce slight diseases, as head-ach, &c. and, when taken very largely, may even put an end to life at once, either by rarefaction of the blood and rupture of the small vessels, as is the case with fixed air, or by oppressing the lungs entirely with their basis, which cannot be thrown out by the breath as in ordinary respiration. Others may affect the electricity of it, or what in this treatise has been called the _vital spirit_, as well as the latent or sensible heat. The consequence of this will be diseases of a more serious nature; for upon this principle in all probability depend not only the secretion and proper regulation of the nervous fluid, but what has been called the _crafts_, or proper consistence of the blood and other fluids. Hence it is possible that such an instantaneous shock may be given to the body, as will not only injure the organization in an irreparable manner, but may be felt throughout the whole body like an electric stroke, even though there be no visible fire, or sensation of burning, as in the case of the Italian priest and others, who perished in such a miserable manner.