362 DISEASES Class IV. i. i. 



of the fecondary part of the train ; and fometimes by decreafed 

 actions of it. So likewife the decreafed actions of the primary- 

 part of a train of afTociate motions are fometimes fucceeded by 

 decreafed actions of the fecondary part, and fometimes by 

 increafed actions of it. The former of thefe fituations is called 

 direct fympathy, and the latter reverfe fympathy. In general I 

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

 is exerted more than natural, it produces direct fympathy in 

 ftrong people, and reverfe fympathy in weak ones, as a full meal 

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

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

 direct fympathy in weak people, and reverfe fympathy in ftrong 

 ones, as on being expofed for a certain length of time on horfe- 

 back in a cold day gives indigeftion and confequent heart-burn 

 to weak people, and ftrengthens the digeftion, and induces con- 

 fequent hunger in ftrong ones. See Sect. XXXV. i. 



This may perhaps be more eafily underftood, by confidering 

 flrength and weaknefs, when applied to animal bodies, as con- 

 fiding in the quantity of fenforial power refiding in the con- 

 tracting fibres, and the quantity of ftimulus applied, as (hewn 

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

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

 the expenditure of fenforial power is for a while leffened, but 

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

 the weakly ftimulated part. Hence in ftrong people, or fuch 

 whofe fibres abound with fenforial power, if the firft tribe of an 

 afTociate train of motions be deprived in part of its accuftomed 

 ftimulus, its action becomes diminifhed ; and the fenforial pow- 

 er becomes accumulated, and by its fuperabundance, or over- 

 flowing as it were, increafes the action of the fecond tribe of 

 the afTociate actions by reverfe fympathy. As expofing the 

 warm fkin for a moderate time to cold air increafes the action 

 of the ftomach, and thus ftrengthens the power of digeftion. 



On the reverfe, when additional ftimulus within certain lim- 

 its is partially applied to parts, which are deficient in refpect to 

 the natural quantity of fenforial power, the expenditure of fen- 

 forial power is increafed, but in a lefs degree than the increafed 

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

 ftrongly-ftimulated organ. Hence in weak people, or fuch 

 whofe fibres are deficient of fenforial power, if the firft tribe of 

 an afTociate train of motions be fubjected for a while to greater 

 ftimulus than ufual, a greater production of fenforial power, or 

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

 by its excefs, or overflowing as it were, increafes the actions of 

 the fecond tribe of the afTociate motions by direct fympathy. 



Thus 



