Sentence:  ... I cannot think it unreaſonable, ... to imagin the ſame natural cauſes may ſometimes act in t'other extreme likewiſe, and model Humane Bodies from a peculiar "Energy" in the ſeminal Principles, or a more perfect and through "concoction" in the "Stomach", and other "Viſcera", whence may proceed a peculiar and extraordinary nutritive faculty in the humours, for the furthering augmentation; or ſtill from ſome other more latent Spring, or ſecret Influence, to ariſe to ſuch a growth as fully to equal twice the heighth of (what we may then properly call) a <WSD>"middling</WSD> ſtature", taking the word in the moſt ſtrict ſenſe. 
Meaning of the word marked with <WSD> tags:  Of intermediate or average size, position, or quality; mediocre.