150 CATENATION SECT. XVIL 3. 2 . 



motion, have the ftrongeft connexion. Thirdly, that of thefe, 

 thofe, which were firft formed, have the (trongeft connexion. 

 Fourthly, that if an animal motion be excited by more than one 

 caufation, affbciation, or catenation, at the fame time, it will be 

 performed with greater energy. 



2. Hence alfo we understand, why the catenations of irrita- 

 tive motions are more ilrongly connected than thofe of the oth- 

 er claftes, where the quantity of unmixed repetition has been 

 equal ; becaufe thry were firft formed. Such are thofe of the 

 fecerning and abforbent fyftems of veiTels, where the action of 

 the gland produces a fluid, which ftimulates the mouths of its 

 correipondent abforbents. The afTociated motions feem to be 

 the next moft ftrongly united, from their frequent repetition ; 

 and where both thefe circumftances unite, as in the vital motions, 

 their catenations are indiiloluble but by the deftrution of the 

 animal. 



3. Where a new link has been introduced into a circle of 

 ahons by fome accidental defeft of ftimulus ; if that defeft of 

 ilimulus be repeated at the fame part of the circle a fecond or 

 a third time, the defective motions thus produced, both by the 

 repeated defet of ftimulus and by their catenation with the 

 parts of the circle of actions, will be performed with lefs and 

 lefs energy. Thus if any perfon is expofed to cold at a certain 

 hour to-day, fo long as to render fome part of the fyftem for 

 a time torpid ; and is again expofed to it at the fame hour to- 

 morrow, and the next day ; he will be more and more afTe&ed 

 by it, till at length a cold fit of fever is completely formed, as 

 happens at the begining of many of thofe fevers, which are 

 called nervous -or low fevers. Where the patient has flight pe- 

 riodical fhiverings and palenefs for many days before the febrile 

 paroxyfm is completely formed. 



4. On the contrary if the expofure to cold be for fo fhort a 

 time, as not to induce any confiderable degree of torpor or qui- 

 efcence, and is repeated daily as above mentioned, it lofes its 

 effeft more and more at every reperirion, till the conftitution 

 can bear it without inconvenience, or indeed without being con- 

 fcious of it. "As in walking into the cold air in froity weather. 

 The fame rule is applicable to increafed ftimulus, as of heat, or 

 vinous fpirit, within certain limits, as is applied in the two lad 

 paragraphs to Deficient Stimulus, as is further explained in Seft. 

 XXXVI. on the Periods of Difeafes. 



5. Where irritation coincides with fenfation to produce the 

 fame catenations of motion, as in inflammatory fevers, they are 

 excited with ftill greater energy than .by the irritation alone. 

 So when children expert to be tickled in play, by a feather light- 



