In the interest of time, I'll quote from an edition of a 15th century Middle English translation of his Latin work instead of trying to translate the Latin, which I won't do all that well in a few minutes. All quotations and page numbers are from Treatises of Fistula in Ano, D'Arcy Power, ed., London, Early English Text Society, 1910.
Sanguis Veneris was one of a few different preparations that could be used several days after surgery to clean and dry the wound. It was so-called because of its redness and sweetness, and was known (says our author) to ladies by the French name "sank damours or sank de pucels" (p. 89) [blood of love, or blood of ladies/young women/whores depending on context]. There is a sense here that it is well-known among women and perhaps sought out by women, but all that isn't spelled out here. There were two different ways to make it, depending on what you had access to and how much your patient could pay. One was to combine an ounce of powdered alkanet with a quart of oil, blended or boiled together (either way). It's to be kept in an earthen or pewter pot. Because its properties are cold and dry, it's good for drying up many kinds of wounds or ulcers and preventing infection (I'm rather freely paraphrasing here). Blended with vinegar and applied to the head, it's good for headache (still p. 89).
The second way to make it goes something like this: take blood from a virgin (or, if one cannot be found, of a damsel of about 18 or 19 years old who was never with child). The blood is to be drawn during the full moon, when the moon is in Virgo and the sun is in Pisces. To this blood, add equal parts "aloes cicotrine," myrrh, and dragon's blood; then add powdered alkanet in an amount equal to the aloes+myrrh+dragon's blood combo. Muddle all this together to make a paste, and then dry it in the sun, storing it for your use.
To use it, take a chunk of it, powder it, and seethe it in olive oil, one ounce per two pounds of oil, or "a quart of a galon,or more if it be nede" (p. 90). Boil it together until the oil is red. When it's red, pull it off the fire, and the resulting mixture is what is applied for medicinal purposes to cool, dry, disinfect, and heal.
N.B. This is medieval medicine, which most medievalists are grateful not to be subjected to, and I am not an herbalist, and there are probably a hundred good reasons not to go mucking about trying to recreate these formulae for use on open wounds, not least of which is the fact that not everybody agrees as to which regionally-available (or available-by-import) plants are being referred to in texts like this. In short: DO NOT MAKE A BATCH OF THIS STUFF AND PUT IT ON AN OPEN WOUND. If you are even *thinking* of trying this based on a blog post you find on the internet, please go above and click on the link to the illustrated manuscript page for a vivid reminder of how different, and how much more unpleasant, medicine was in the middle ages. However, by medieval principles of sympathetic magic, the doctrine of signatures, and humoural theory, you could certainly make a case for using such a mixture as a spiritual or magical oil as part of spell or altar work to effect healing of conditions brought upon by an excess of heat and moisture (fever, for instance, maybe gout, other types of "hot, wet" illnesses). If the subtext I perceive here is really meant to be here, this could also be used in any type of working to draw love, incite lust, and gain romantic attention.
After surgery, flesh could be regenerated and scarring induced by using various preparations, including myrrh, aloes, dragon's blood, Arabian gum, something called sarcocolla, pomegranate bark, and/or flour, mixed with egg-white and sanguis veneris or mel rosat. Mel rosat is made by mixing honey and the juice from red rose petals, and is smeared onto cloth and laid on the wound. (84-87 and passim)
 I am not advising anyone to go around poking 18-year-olds with lancets, but just for the sake of interest, this Friday, Feb 18, 2011, you will have a full moon with the Sun in Pisces and the Moon in Virgo. Where I live, the moon is officially full on the 18th, the Moon enters Virgo at 4:40 am, and the Sun enters Pisces at 7:26 pm, so you would have to make your Sanguis Veneris after 7:26 pm EST and, I think, ideally before 3-ish a.m. on the 19th. Now, if you're a client or customer of mine, you may have written me before with questions about moon phases and astrological signs in your rootwork and had me give you short and even dismissive answers - if the astrology suits your needs, feel free to time your work this way, but in general, I make the timing fit my needs rather than holding off on my work to wait on some moon phase or conjunction, and I rarely advise clients to wait around for the moon if their work really needs doing. The exception would be the preparation of some kind of ultra-special, preplanned talisman, amulet, or formula that you can only make every once in a while - like my Three Kings Oil which I make annually at the Feast of the Epiphany, or a gambling luck charm made on 7/7/2007, or some complicated astrological talisman designed to get success flowing in your life, which has to be done at a certain time of the year or even during a rarer astrological event, for which you have planned in advance as something "beyond the scope of day-to-day conjure remedies." But I offer this as a curiosity for those of you interested in reading such things, and mention the upcoming perfect timing for those who like to make their own preparations.