PHYSIOLOGY. 113 



cited by which they are contracted, rendered innocent or expell- 

 ed. This is what has been termed the vis medicatrix naturae ; 

 but, as this is in every book, I do not think it necessary to in- 

 sist upon it here. This constitution of the animal economy we 

 have called NATURE, from the time of Hippocrates to the pre- 

 sent ; it is thus directed to the preservation, or to the remedy- 

 ing the faults of the system. We think it safer than any 

 other term that has been applied than the whimsical one of an 

 Archaeus, of a Praeses systematis nervosi, or of the rational soul 

 of Stahl, which is liable to dispute." 



CXXI. It is in consequence of this constitution, that not 

 only impulse, and other causes which may be supposed to pro- 

 duce motion, do accordingly excite motions in the animal eco- 

 nomy ; but that also many causes, which seem to diminish mo- 

 tion, do, however, produce an increase of motion in animal 

 bodies. Thus, several passions which, in their first tendency, di- 

 minish motion, several propensities arising from debility and diffi- 

 culty of action, the absence of usual impressions, evacuations, and 

 other causes of relaxation, cold and narcotic powers, are all of 

 them causes of considerable motions arising in the animal system. 



" This proposition, if true, is to me one of the most cu- 

 rious and important in our system : that the animal econ- 

 omy has powers in itself, and, in consequence of its own pe- 

 culiar constitution, resists and obviates various injuries, and not 

 only so as to prevent their effects, but that when these are pro- 

 duced, the constitution remedies these very evils, and restores 

 health. This, in general, to a certain extent, is universally 

 acknowledged. I shall speak in another place of its limits : I 

 cannot go far in the theory ; but this is an obvious reflection, 

 that if the causes of the injuries are of themselves of an active 

 nature, and do excite motions, we may imagine that in conse- 

 quence of the constitution, these motions have a tendency to re- 

 move the effects of the injuries ; but it is difficult to find how 

 any powers that diminish motion should prove active with re- 

 gard to the system, and excite its latent powers. I give an ex- 

 ample : opium, as proved by many experiments, has the power 

 of diminishing sensibility and irritability, and can go the 

 length of extinguishing the vital powers altogether; but this 

 same opium often acts as a stimulant, increasing the motion of 



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