DISEASES CLASS IV. 1. 1. 



of the secondary part of the train; and sometimes by decreased 

 actions of it. So likewise the decreased actions of the primary 

 part of a train of associate motions are sometimes succeeded by 

 decreased actions of the secondary part, and sometimes by 

 increased actions of it. The former of these situations is called 

 direct sympathy, and the latter reverse sympathy. In general I 

 believe, where the primary part of the train of associated motions 

 is exerted more than natural, it produces direct sympathy in 

 strong people, and reverse sympathy in weak ones, as a full meal 

 makes some people hot, and others chill. And where the pri- 

 mary part of the train is exerted less than natural, it produces 

 direct sympathy in weak people, and reverse sympathy in strong 

 ones, as on being exposed for a certain length of time on horse- 

 back in a cold day gives indigestion and consequent heart-burn 

 to weak people, and strengthens the digestion, arid induces con- 

 sequent hunger in strong ones. See Sect. XXXV. 1 . 



This may perhaps be more easily understood, by considering 

 strength and weakness, when applied to animal bodies, as con- 

 sisting in the quantity of sensorial power residing in the con- 

 tracting fibres, and the quantity of stimulus applied, as shewn 

 in Sect. XII. 2. 1. Now when defective stimulus, within certain 

 limits, is partially applied to parts subject to perpetual motion, 

 the expenditure of sensorial power is for a while lessened, but 

 not its general production in the brain, nor its derivation into 

 the weakly stimulated part. Hence in strong people, or such 

 whose fibres abound with sensorial power, if the first tribe of an 

 associate train of motions be deprived in part of its accustomed 

 stimulus, its action becomes diminished, and the sensorial power 

 becomes accumulated, and by its superabundance, or overflowing 

 as it were, increases the action of the second tribe of the associate 

 actions by reverse sympathy. As exposing the warm skin for 

 a moderate time to cold air increases the action of the stomach, 

 and thus strengthens the power of digestion. 



On the reverse, when additional stimulus within certain limits 

 is partially applied to parts, which are deficient in respect to 

 the natural quantity of sensorial power, the expenditure of sen- 

 sorial power is increased, but in a less degree than the increased 

 production of it in the brain, or its increased derivation into the 

 strongly-stimulated organ. Hence in weak people, or such 

 whose fibres are deficient of sensorial power, if the first tribe of 

 an associate train of motions be subjected for a while to greater 

 stimulus than usual, a greater production of sensorial power, or 

 a greater derivation of it into the stimulated parts occurs; which 

 by its excess, or overflowing as it were, increases the actions of 

 the second tribe of the associate motions by direct sympathy. 



