I delved a bit (so to speak) into hot glue for an article in the
Player Piano Group bulletin a year or two back.

Hot glue is simply gelatine, traditionally made from animal bones
and skin, processed to denature the collagen into gelatine.  Different
processing affected things such as the residual amount of fat in the
mixture -- its presence making the glue cloudy.  There's plenty of
detail on the Web about how hot glue used to be made, mostly verbatim
repeats of out-of-copyright Encyclopedia Britannica entries.

It is entirely feasible to use food-grade gelatine for hot glue. [*]
These days concerns about use of cattle offcuts have largely (if
not entirely) caused a shift towards the use of fish skin for food
gelatine, this being available in vast bulk and of no use for anything
else, and more widely acceptable as a foodstuff.  I really cannot see
this ever being banned, so I'm sure there's plenty of life in this most
traditional of products.

The type of collagen used to make the gelatine affects the setting
properties of the resulting solution.  Fish, being cold-blooded, have
collagen that denatures at a much lower temperature than hot-blooded
animals, hence the "fish glues" that are liquid at room temperature.
The art world use rabbit-skin hot glue as the base for gesso.

Julian Dyer

 [* Indeed, a Wikipedia article says "Animal glues such as hide glue
 [ are essentially unrefined gelatin."  -- Robbie