III.  The associated trains of our ideas may have sympathies, and their primary and secondary parts affect each other in some manner similar to those above described; and may thus occasion various curious phenomena not yet adverted to, besides those explained in the Sections on Dreams, Reveries, Vertigo, and Drunkenness; and may thus disturb the deductions of our reasonings, as well as the streams of our imaginations; present us with false degrees of fear, attach unfounded value to trivial circumstances; give occasion to our early prejudices and antipathies; and thus embarrass the happiness of our lives.  A copious and curious harvest might be reaped from this province of science, in which, however, I shall not at present wield my sickle.

* * * * *

SECT.  XXXVI.

OF THE PERIODS OF DISEASES.

I. Muscles excited by volition soon cease to contract, or by sensation, or by irritation, owing to the exhaustion of sensorial power.  Muscles subjected to less stimulus have their sensorial power accumulated.  Hence the periods of some fevers.  Want of irritability after intoxication. II. 1. Natural actions catenated with daily habits of life. 2. With solar periods.  Periods of sleep.  Of evacuating the bowels. 3. Natural actions catenated with lunar periods.  Menstruation.  Venereal orgasm of animals.  Barrenness. III. Periods of diseased animal actions from stated returns of nocturnal cold, from solar and lunar influence.  Periods of diurnal fever, hectic fever, quotidian, tertian, quartan fever.  Periods of gout, pleurisy, of fevers with arterial debility, and with arterial strength, Periods of rhaphania, of nervous cough, hemicrania, arterial haemorrhages, haemorrhoids, haemoptoe, epilepsy, palsy, apoplexy, madness. IV. Critical days depend on lunar periods.  Lunar periods in the small pox.

I. If any of our muscles be made to contract violently by the power of volition, as those of the fingers, when any one hangs by his hands on a swing, fatigue soon ensues; and the muscles cease to act owing to the temporary exhaustion of the spirit of animation; as soon as this is again accumulated in the muscles, they are ready to contract again by the efforts of volition.

Those violent muscular actions induced by pain become in the same manner intermitted and recurrent; as in labour-pains, vomiting, tenesmus, strangury; owing likewise to the temporary exhaustion of the spirit of animation, as above mentioned.

When any stimulus continues long to act with unnatural violence, so as to produce too energetic action of any of our moving organs, those motions soon cease, though the stimulus continues to act; as in looking long on a bright object, as on an inch-square of red silk laid on white paper in the sunshine.  See Plate I. in Sect.  III. 1.