On the contrary, where less of the stimulus of volition, sensation, or irritation, have been applied to a muscle than usual; there appears to be an accumulation of the spirit of animation in the moving organ; by which it is liable to act with greater energy from less quantity of stimulus, than was previously necessary to excite it into so great action; as after having been immersed in snow the cutaneous vessels of our hands are excited into stronger action by the stimulus of a less degree of heat, than would previously have produced that effect.

From hence the periods of some fever-fits may take their origin, either simply, or by their accidental coincidence with lunar and solar periods, or with the diurnal periods of heat and cold, to be treated of below; for during the cold fit at the commencement of a fever, from whatever cause that cold fit may have been induced, it follows, 1.  That the spirit of animation must become accumulated in the parts, which exert during this cold fit less than their natural quantity of action. 2.  If the cause producing the cold fit does not increase, or becomes diminished; the parts before benumbed or inactive become now excitable by smaller stimulus, and are thence thrown into more violent action than is natural; that is a hot fit succeeds the cold one. 3.  By the energetic action of the system during the hot fit, if it continues long, an exhaustion of the spirit of animation takes place; and another cold fit is liable to succeed, from the moving system not being excitable into action from its usual stimulus.  This inirritability of the system from a too great previous stimulus, and consequent exhaustion of sensorial power, is the cause of the general debility, and sickness, and head-ach, some hours after intoxication.  And hence we see one of the causes of the periods of fever-fits; which however are frequently combined with the periods of our diurnal habits, or of heat and cold, or of solar or lunar periods.

When besides the tendency to quiescence occasioned by the expenditure of sensorial power during the hot fit of fever, some other cause of torpor, as the solar or lunar periods, is necessary to the introduction of a second cold fit; the fever becomes of the intermittent kind; that is, there is a space of time intervenes between the end of the hot fit, and the commencement of the next cold one.  But where no exteriour cause is necessary to the introduction of the second cold fit; no such interval of health intervenes; but the second cold fit commences, as soon as the sensorial power is sufficiently exhausted by the hot fit; and the fever becomes continual.