The Kitzur Shulchan Aruch was written in the 1800s, based on the Shulchan Aruch, which was written in the 1500s. This chapter discusses the medical treatments of the times, some of which may now be discredited. Here, we only address the permissibility of those treatments on Shabbos, not their medical effectiveness. Please consult your own rabbi regarding matters of medical treatment on Shabbos. In case of serious illness or injury, seek medical attention!
91:11 One may not place a cloth on a bleeding wound because the blood colors it; even more so one may not use a red cloth, since this improves the color. One may likewise not squeeze a wound in order to extract the blood. What he should do is to wash the wound in water to remove the blood, and then wrap a rag around it. If the blood doesn’t stop from washing, he should place spider webs on it and then wrap a rag around it. Some authorities do not permit this because spider webs have medicinal value. Therefore, if possible, one should ask a non-Jew to do this. [Editor’s note: while not currently in vogue, spider webs are a traditional treatment that has been used for hundreds of years; they are rich in vitamin K, which helps blood to clot.]
91:12 One may not open an abscess in order to widen the wound as doctors do when they treat it as this is the work of a doctor. If one opened it only to remove pus that’s causing him distress, and he doesn’t care if it closes up immediately, it is permitted because it caused him distress. (This is true even if there is also blood there since any blood that will come out in this instance is not the result of a wound – Mishnah Brurah 328:89.) One may only pierce it with something like a needle but not with his fingernails because that removes some of the skin around the abscess, which is prohibited on Shabbos. Since using a needle raises the concern that he may intend to leave it open in order to remove pus from it later, it is preferable to have this done by a non-Jew where possible.