Responsa zu Wajikra 7:39

2. Now we turn to the question as to whether a Jewish patient may, according to Jewish law, use such a bone; or, to put the question more widely, whether he may use the skin of another person for healing, as is done in burns. May he use the blood of another person, as is now a widespread practice, etc.? Almost all of these questions have been discussed, in some form, in the older legal literature. There is, for example, a prohibition against the use of the blood of a human being. Yet the law is careful to define the nature of this prohibition. The Bible, in Leviticus, 7:26 says: "Thou shalt not eat the blood of bird or domestic animal." In other words, there is a specific prohibition against eating the blood of these kosher animals. Therefore their meat is soaked and salted, etc. This special and additional prohibition against the blood applied only to these animals for we might imagine that as their flesh is permitted, so is their blood; but the blood of other animals which are entirely prohibited, dom mahalche shenayim, the blood of bipeds or man, does not need to be given this special blood prohibition by the Torah. (See Sifra Leviticus at the end of Parsha 10; also Talmud, Kerisos 21 b.) The question is of some practical importance, for example, in the discussion as to whether a man may swallow the blood from his own bleeding teeth, etc. Of course, the blood of human beings is prohibited with a general prohibition, that the human body is forbidden for food, hence there is no need for a special prohibition as with cattle and birds. So Maimonides decides that the prohibition of blood of bipeds is a prohibition, but on rabbinic grounds. (Yad, Ma'acholos Asuros VI, #2.)