OP THE VITAL POWERS. 17 



SECT. IV. 



OF THE VITAL POWERS IN GENERAL, AND PARTICU- 

 LARLY OF CONTRACTILITY. 



29. Hitherto we have spoken of the solids as 

 the constituents of the system ; we now shall view them 

 as endowed with vitality, — capable of receiving the 

 agency of stimuli, and of performing motions. 



30. Although vitality* is one of those subjects which 

 are more easily known than defined, and usually indeed 

 rendered obscure rather than illustrated by an attempt 

 at definition, its effects are sufficiently manifest and 

 ascribable to peculiar powers only. The epithet vital 

 is given to these powers, because on them so much 

 depend the actions of the whole body during life and 

 of those parts which for a short time after death pre- 

 serve their vitality, that they are not referrible to any 

 qualities merely physical, chemical, or mechanical. 



31. The latter qualities, however, are of great im- 

 portance in our economy. By physical powers, de- 

 pendent on the density and figure of the humours of the 

 eye, the rays of light are refracted to the axis ; by me- 

 chanical, the epiglottis is elastic ; by chemical affinity, 

 the changes of respiration are effected. But the perfect 

 difference of these dead powers from those which we 



* A host of authors on the vital powers will be found in Fr. Hildebrandt's 

 Lehrbuch der Physiologic, p. 54 sq. edit. 2. 1809. To whom we may add 

 E. BarteFs Systemat. Entwurf einer allgemcinen Biologic Franckfurt. 1808 : 

 and J. B. P. A. Lamarck's Philosophic Zoologiqiie. Paris. 1809. 11 vols. 8vo. 



C 



