Sentence:  "To make Capons" ... [S]ome for this Purpoſe make it their Buſineſs after Harveſt-time to go to Markets for buying up Chickens, and between "Michaelmas" and "All-hollantide" caponize the Cocks, when they have got large enough to have Stones ["i.e.", testes] of ſuch a Bigneſs that they may be pulled out; for if they are too little, it <WSD>can't</WSD> be done; ... 
Meaning of the word marked with <WSD> tags:  Often with "be": is logically impossible.