Sentence:  For Spirits when they pleaſe / Can either Sex aſſume, or both ; ſo ſoft / And uncompounded is their <WSD>Eſſence</WSD> pure, / Not ti'd or manacl'd with joynt or limb, / Nor founded on the brittle ſtrength of bones, / Like cumbrous fleſh... 
Meaning of the word marked with <WSD> tags:  Constituent substance.