I. 1. Sympathy or consent of parts.  Primary and secondary parts of an associated train of motions reciprocally affect each other.  Parts of irritative trains of motion affect each other in four ways.  Sympathies of the skin and stomach.  Flushing of the face after a meal.  Eruption of the small-pox on the face.  Chilness after a meal. 2. Vertigo from intoxication. 3. Absorption from the lungs and pericardium by emetics.  In vomiting the actions of the stomach are decreased, not increased.  Digestion strengthened after an emetic.  Vomiting from deficiency of sensorial power. 4. Dyspnoea from cold bathing.  Slow pulse from digitalis.  Death from gout in the stomach. II. 1. Primary and secondary parts of sensitive associations affect each other.  Pain from gall-stone, from urinary stone, Hemicrania.  Painful epilepsy. 2. Gout and red face from inflamed liver.  Shingles from inflamed kidney. 3. Coryza from cold applied to the feet.  Pleurisy.  Hepatitis. 4. Pain of shoulders from inflamed liver. III. Diseases from the associations of ideas.

I. 1.  Many synchronous and successive motions of our muscular fibres, and of our organs of sense, or ideas, become associated so as to form indissoluble tribes or trains of action, as shewn in Section X. on Associate Motions.  Some constitutions more easily establish these associations, whether by voluntary, sensitive, or irritative repetitions, and some more easily lose them again, as shewn in Section XXXI. on Temperaments.

When the beginning of such a train of actions becomes by any means disordered, the succeeding part is liable to become disturbed in consequence, and this is commonly termed sympathy or consent of parts by the writers of medicine.  For the more clear understanding of these sympathies we must consider a tribe or train of actions as divided into two parts, and call one of them the primary or original motions, and the other the secondary or sympathetic ones.

The primary and secondary parts of a train of irritative actions may reciprocally affect each other in four different manners. 1.  They may both be exerted with greater energy than natural. 2.  The former may act with greater, and the latter with less energy. 3.  The former may act with less, and the latter with greater energy. 4.  They may both act with less energy than natural.  I shall now give an example of each kind of these modes of action, and endeavour to shew, that though the primary and secondary parts of these trains or tribes of motion are connected by irritative association, or their previous habits of acting together, as described in Sect.  XX. on Vertigo.  Yet that their acting with similar or dissimilar degrees of energy, depends on the greater or less quantity of sensorial power, which the primary part of the train expends in its exertions.