SECT. XXIX. 1 1. 3. ABSORBENTS. a% 



ural quantity of their adapted ftimuli. Thus the eye is inca- 

 pable of feeing objects in an obfcure room, though the iris is 

 quite dilated, afrer having been expofed to the meridian fun. 



3. There is a third law of irritation, that all the parts of our 

 bodies, which have been lately fubjecled to lefs ftimulus, than 

 thf y have been accuflomed to, when they are expofed to their 

 uiual quantity of ftimulus, are excited into more energetic mo- 

 tions ; thus when we come from a dufky cavern into the glare 

 of day-light, our eyes are dazzled ; and after emerging from the 

 cold bath, the fkin becomes warm and red. 



4. There is a fourth law of irritation, that all the parts of our 

 bodies, which are fuojecled to (till ftronger ftimuli for a length 

 of time, become torpid, and refufe to obey even thefe ftronger 

 ftimuli ; and thence do their offices very imperfectly ^-Thus, if 

 any one looks earneftly for fome minutes, on an area, an inch di- 

 ameter, of red fiik, placed on a (heet of white paper, the image 

 of the filk will gradually become pale, and at length totally vanifh. 



5. Nor is it the nerves of fenfe alone, as the optic and audi- 

 tory nerves, that thus become torpid, when the ftimulus is with- 

 drawn or their irritability decrcafed ; but the motive mufcles, 

 when they are deprived of their natural ftimuli, or of their irri- 

 tability, become torpid and paralytic ; as is feen in the tremu- 

 lous hand of the drunkard in a morning ; and in the awkward 

 ftep of age. 



The hollow mufcles alfo, of which the various veflels of the 

 body are conftruded, when they are deprived of their natural 

 ftimuli, or of rheir due degree of irritability, not only become 

 tremulous, as the arterial puifations of dying people j but alfo 

 frequently invert their motions, as in vomiting, in hyfteric fu fib- 

 cations, and diabetes above defcribed. 



I muft beg your patient attention, for a few moments, whilft 

 I endeavour to explain, how the retrograde actions of our hol- 

 low mufcles are the confequence of their debility ; as the tremu- 

 lous actions of the folid mufcles are the confequence of their de- 

 biliy. When, through fatigue, a mufcle can act no longer; the 

 antagoniil mufcles, either by their inanimate elafticity, or by 

 their animal aclion, draw the limb into a contrary direction : in 

 the folid mufcles, as thofe of locomotion, their actions are aflb- 

 ciated in tribes, which have been accuftomed to fynchronous ac- 

 tion only ; hence when they are fatigued, only a (ingle contrary 

 effort takes place ; which is either tremulous, when the fatigued 

 rmifcles are again immediately brought into action ; or it is a 

 pamiiculution, or ftretching, where they are not immediately 

 Hgain brought into action. 



Now the motions of the hollow mufcle?, as they in general 



propel 



