382 ESSAY III . 
ternal Caufe that peculiar Contexture is deftroyed , and Death enfues . As the continual Dilatations and Contrarions of the Heart and Arteries , by which the Blood is maintained in its circulatory Motion , can no ways be either intended or remitted by the Power of Thought ; fo that peculiar Mechanifm , by which they continue thofe Motions when once begun muft be fomething very different from that Difpofition of the Mufclcs , which enables them to reft or move , juft as the Thinking Faculty pleafes to direâ : them ; the Motions of the former being the necefiary Refult of the peculiar Difpofitions of their component Parts , and the latter only fuch as they fall into according to the Determinations of an ternal Agent . This laft Enquiry , hath employed a great many Heads , and produced great Variety of Hypothefes and Conjectures , but very little to the fatisfaélion of fuch who have been unprejudiced and fincere Searchers after Truth , until Application hath been made to thofe proper and only Means , by which the Operations of all Phyfical Agents are to be determined , which is upon Mechanical Principles ; and upon thefe , Steno and Borelli have had the Honour of making a very good Beginning , upon whofe Foundations , Dr Bernoulli of Baftl , ( whofe Account of Mufcular Motion , printed in the Leipjic Tranfaclions in 1694 , hath been lately pub - lifhed in London by Dr Mead under the Title of Dijfertatio de Motu Mttfculorum ) and fince him Dr James Keil has improved much to the fatif - faftion of thofe who are not to be contented without fuch Convi & ion and Demonftration as the' Nature of fuch Things will admit of , and do quire . 
It is well known , that any Membrane or Veflel may be feparated and divided into very fmall Fibres or Threads , I mean when it is juft taken out of the i Body ,