Comparatively recently dog manure was collected and used in early stages of making leather
allegeely because residual pancreatic enzymes removed unwanted proteins from hides
New Scientist for Aug 13 Aug 02 p.27 states that though it is in some texts called "pure" it
seems logical to believe this is confusion with "puer" as boys were principal collectors thereof.

Winchester (Professor and Madman) called dog manure colected for leather tanning pure, modern american dictionaries don't include this defination, but i suspect the OED still does..
i think i would trust them.

Simon Manchester has been known to err. Here is a sentence from an encyclopedia article
"After pulling down the goods to a soft, silky condition by bating or puering, it is
necessary, after scudding, to plump them up again and bring them into a clean and fit
condition for receiving the tan."

There is logic to "puer", no logic to "pure". If figures that clerks knowing Latin used "puer"
and clerks who did not copied the sound as "pure".

Here is URL to encyclopedia article. It is very long, and you have to scroll down halfway to find
the quote given above.
http://28.1911encyclopedia.org/L/LE/LEATHER.htm

I have encountered several surnames that were originally job titles. In my own genealogy, the
name "Thayer" meant someone who made a "tea" pronounced "tay" out of bark for tanning leather.
The name "Scudder" derived froms specialty of scraping hair off hide after treatment had loosened it.
And the name "Bate" referred to speciallist in treatment to remove proteins that do not contribute
to strength of leather.(Meaning using less revolting agents than "puer".)