Chapter 46: 1-3 Laws Pertaining to Forbidden Foods
1. Blood which is found in eggs is prohibited. Furthermore, at times, the entire egg may be prohibited. Therefore, eggs should be checked before being used for cooking.
2. The blood of a fish is permitted. However, it is forbidden if it is collected in a receptacle, lest it create a wrong impression. Since this is the reason for the prohibition, if the blood is clearly recognizable as coming from fish - e.g., it is served with scales - it is permitted to be used.
3. [Once blood leaves a person's body, it is forbidden. Therefore, if a person with bleeding gums] bites into a loaf of bread and some blood is left on the bread, the portion with the blood must be cut off and disposed of. However, during the week, one is allowed to suck the blood [from the gums], since it has not left the body. (However, on the Sabbath this is forbidden, as will be explained in Chapter 80, Law 54.)