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SECT.  XII.

OF STIMULUS, SENSORIAL EXERTION, AND FIBROUS CONTRACTION.

I. Of fibrous contraction. 1. Two particles of a fibre cannot approach without the intervention of something, as in magnetism, electricity, elasticity.  Spirit of life is not electric ether.  Galvani’s experiments. 2. Contraction of a fibre. 3. Relaxation succeeds. 4. Successive contractions, with intervals.  Quick pulse from debility, from paucity of blood.  Weak contractions performed in less time, and with shorter intervals. 5. Last situation of the fibres continues after contraction. 6. Contraction greater than usual induces pleasure or pain. 7. Mobility of the fibres uniform.  Quantity of sensorial power fluctuates.  Constitutes excitability. II.  Of sensorial exertion. 1. Animal motion includes stimulus, sensorial power, and contractile fibres.  The sensorial faculties act separately or conjointly.  Stimulus of four kinds.  Strength and weakness defined.  Sensorial power perpetually exhausted and renewed.  Weakness from defect of stimulus.  From defect of sensorial power, the direct and indirect debility of Dr. Brown.  Why we become warm in Buxton bath after a time, and see well after a time in a darkish room.  Fibres may act violently, or with their whole force, and yet feebly.  Great exertion in inflammation explained.  Great muscular force of some insane people. 2. Occasional accumulation of sensorial power in muscles subject to constant stimulus.  In animals sleeping in winter.  In eggs, seeds, schirrous tumours, tendons, bones. 3. Great exertion introduces pleasure or pain.  Inflammation.  Libration of the system between torpor and activity.  Fever-fits. 4. Desire and aversion introduced.  Excess of volition cures fevers. III.  Of repeated stimulus. 1. A stimulus repeated too frequently looses effect.  As opium, wine, grief.  Hence old age.  Opium and aloes in small doses. 2. A stimulus not repeated too frequently does not lose effect.  Perpetual movement of the vital organs. 3. A stimulus repeated at uniform times produces greater effect.  Irritation combined with association. 4. A stimulus repeated frequently and uniformly may be withdrawn, and the action of the organ will continue.  Hence the bark cures agues, and strengthens weak constitutions. 5. Defect of stimulus repeated at certain intervals causes fever-fits. 6. Stimulus long applied ceases to act a second time. 7. If a stimulus excites sensation in an organ not usually excited into sensation, inflammation is produced. IV.  Of stimulus greater than natural. 1. A stimulus greater than natural diminishes the quantity of sensorial power in general. 2. In particular organs. 3. Induces the organ into spasmodic actions. 4. Induces the antagonist fibres into action. 5. Induces the organ into convulsive