VI 
PREFACE. 
federation of the Ufe of the Interftitial Air, and 
its Count er-afl ion with that contain d in the ner- 
vous and mufcular Syftem * and (%J upon my 
Obfervation of the Circulation of the Bloody 
in the minute V ffels of fever al Animals , and 
their parallel dJireclion to other Fibres : All 
which P articulars are my own Bifcoveries ; 
and, being duly connected , feem to me the moft 
likely , that have hitherto appeared , to give 
fame Eight info the Nature of Mufcular 
Motion. 
V. 
! Thefe Things naturally lead me to mifider 
the animal Body as a Machme confeftmg of Two 
complete Sets or Syfeems of Organs , each per - 
feSl in itfelf and each containing a Fluid pecu- 
liar to itfelf and different from the other . The 
firfl of thefe is that of the Ladteals, Blood- vef- 
fels, and Lymphatics, continued to each other , 
and containing its proper Fluids the Mafs of 
Blood, and its derivative ffuices ; and the 
other is the Nervous and Mufcular Syftem, 
which 
