SECT. XXXII. 6. DISEASES OF IRRITATION. 43 r 



of the momentum of the particles of the circulating 

 blood, and thus tends to induce quiefcence : as is 

 feen in hylleric cafes, and chlorous, and the other, 

 difeafes of fedentaiy people. 



4. The velocity ol the particles of the blood in 

 certain circumilances is increafed by venefe&ion, 

 which, by removing a part of it, diminishes the re- 

 iiftance to the motion of the other part, and hence 

 jthe momentum of the particles of it is increafed. 

 This may be eaiily undeiftood by confidering it in 

 the extreme, fmce, if the refiftance was greatly in- 

 creafed, fo as to overcome the propelling power, 

 there could be no velocity, and in confequence no 

 momentum at all. From this circumftance arifes 

 that curious phenomenon, the truth of which I 

 nave been more than once witnefs to, that vene- 

 leclion will often iqftantaneoufly relieve thofe ner- 

 vous pains, which attend the cold periods of hyfle- 

 lic, afthmatic, or epileptic difeaies ; and that even 

 where large dofes of opium have been in vain ex- 

 hibited. In thefe cafes the pulfe becomes ilronger 

 after the bleeding, and the extremities regain their 

 natural warmth ; and an opiate then given a6ts 

 with much more certain effecl:. 



VI. There is another caufe, which feems pccafi- 

 pnally to induce quiefcence into fome part of 

 our fyftem, I mean the influence of the fun, ^nd 

 moon; the attraction of thefe luminaries., by de- 

 creafing the gravity of the particles of the blood, 

 cannot aifeft their momentum, as their vis inertia: 

 remains the fame ; but it may neverthelefs produce 

 fome chemical change in them, becaufe whatever 

 affe&s the general attractions of the particles of 

 matter may be fuppofed from analogy to affect 

 their fpecific attradions or affinities : and thus the 

 flimulus of the particles of blood may be dimi- 

 nifhed, though not their momentum. As the tides 

 of the fea obey the fouthing and northing of the 



moon 



