OF THE VITAL POWERS. 27 



57. The vital powers will be hereafter separately con- 

 sidered, under the distinct heads of our subject : — The 

 nisus formativus under the head of Generation ; irrita- 

 bility under that of the Muscles ; sensibility under that 

 of the Nervous System ; the vita propria whenever 

 occasion requires. 



58. Besides our former brief remarks (40) upon con- 

 tractility, a few more minute will at present be very 

 appropriate. 



It prevails universally,(40) wherever the mucous tela 

 is discoverable. 



It is consequently most abundant in parts destitute of 

 proper parenchyma, but composed almost entirely of 

 mucous tela, v.c. in certain membranes : for no one will 

 deny their contractility, who reflects upon the spastic 

 motions of the dartos, the male urethra, or the gall 

 bladder, which during death is always closely contracted 

 upon any calculi it may contain. 



It appears also in those viscera which consist chiefly 

 of this tela, v. c. in the lungs, whose external surface 

 we have found on living dissection very contractile; but 

 by no means, as Varnier asserted, truly irritable. (B) 



The presence of contractility even in the bones, is 

 demonstrated by the shrinking of the alveoli after the 

 loss of the teeth, and by the process of necrosis, by 

 which the new bone, when the dead portion is extricated 

 from its cavity, contracts to its natural size and figure. 



The vitreous substance of the teeth, being destitute of 

 this tela (22), possesses no contractility, as I think ap- 

 pears from the circumstance of its not shrinking, like 

 the alveoli, if a portion is separated by caries or 

 fracture. 



59. This contractility of the mucous tela is the chief 



