I have a copy of that particular book, which I acquired as it was relevant to my PhD. Original copies are rather rare, and copies in good condition are very valuable (mine was recovered at some point in plain modern bindings, which allowed me to actually afford it). In terms of the contents, the book is pretty dull; reprints of tales of flogging which previously appeared in various publications. Flagellation and the Flagellants by James Glass Bertram is far better, though you would have to be a serious fetishist to find any erotic interest in either book.
Studying for a PhD is, of course, the most expensive and least efficient means of obtaining access to obscure pseudo-pornography.
There is a bit of an interesting backstory to this in regards to how the British Library catalogues its supposedly erotic books. The backbone of the library's collection in this area came from the donation of the private collection of Pisanus Fraxi, and most of his collection remains within the so-called "private case". But the collection was slightly arbitrary to begin with, and the curation was not great, so you might have to delve into this collection if you want to read about mid-Victorian attitudes on teaching Latin to schoolgirls, simply because this was amongst the works on Fraxi's bookshelf. Meanwhile, nothing has been added to the private case since 1990, so, for instance, the modern translations of Krafft-Ebing's Psychopathia Sexualis sit in the British Library's general collection.
This wouldn't matter so much, except for the reading conditions imposed. If a work sits in the general collection, you can, for example, read it in the Humanities 2 reading room, with light and air, have breaks if needed, and generally have a good research experience. Conversely, if you are viewing works in the private case, you have to collect them from a specific (under-manned) counter in the Rare Books reading room, read them at some sub-par desks near the music assistance counter, and you have to remain with the works at all times. The general experience means that most sensible researchers avoid using works from the private case, simply because you have to work with them under annoying conditions.
There's been a different version of Cleopatra bathing in asses milk doing the rounds for quite a while, the alternate suggestion being that she was bathing instead in semen .. I find that hard to believe unless she had people 'bashing one out' over her while she was in a bath tub .. there's a few sites that talk about this if you search.
Phew, that's a relief. When I read of the option for 'traditional' milk, my mind was boggling with all sorts of images. Was she using milk from a carton? Powdered? Expressing (though she looks too old for that)? Thank goodness it was all just a setup, however, I've no doubt there probably are some who enjoy such activities and photograph their endeavours. Rule 34 of the Internet and all that.