ONE MAY NOT DO BUSINESS WITH ISURIM [Isurim: business]
Even though it says "Kol Nefesh Michem Lo Sochal Dam," one may benefit from blood, for is equated to water - "Lo Tochalenu Al ha'Aretz Tishpechenu ka'Mayim";
Just like water is permitted, blood is permitted.
22b: Even though it says "v'Lo Sochal ha'Nefesh Im ha'Basar", one may benefit from Ever Min ha'Chai, for it is equated to blood - "Rak Chazak l'Vilti Achol ha'Dam Ki ha'Dam Hu ha'Nefesh."
23a - Question: Regarding Sheratzim it says "Sheketz Hu Lo Ye'achel," yet one may benefit from them!
(Mishnah): If hunters of Chayos, birds and fish happened to catch Tamei species, they may sell them to Nochrim.
Answer: There is different, for it says "Lachem". They are yours (to benefit from them).
Question: If so, it should be permitted to hunt them l'Chatchilah!
Answer: It says "Yihyu" - they retain their initial status.
(Beraisa - R. Yosi ha'Glili): One might have thought that Chelev is permitted only for needs of Hekdesh, but not for Chulin uses. "[V'Chelev...] Ye'aseh l'Chol Melachah" permits even Chulin uses;
Bechoros 6b - Question: What is the source that Tahor milk is permitted? (Perhaps it is Ever Min ha'Chai!)
Answer: We learn from "v'Dei Chalev Izim l'Lachmecha..." (that one may subsist on milk)!
Rejection: Perhaps the verse teaches that one will sell the milk (to Nochrim)!
Shevi'is 7:3 (Mishnah): One may not do business with Peros Shemitah, Bechoros, Terumah, Neveilos, Treifos, Sheratzim u'Rmasim.
Rambam (Hilchos Ma'achalos Asuros 8:16): Any thing that one may not eat but one may benefit from it, one may not do business with it or intend to do his Melachah with it, except for Chelev, for it says "it may be used for any Melachah." Therefore, one may not do business with Neveilos, Treifos, Sheratzim u'Rmasim.
Rambam (18): The general rule is, one may not do business with anything that the Torah forbids. One may do business with anything forbidden mid'Rabanan, whether it is a Safek or Vadai.
Tosfos (Bava Kama 82b DH Lo): The Yerushalmi permits doing business with donkeys and camels because they are for Melachah.
Terumas ha'Deshen (200): May one lend to Nochrim on Ribis if he gives sides of pigs for collateral? No. The Mishnah forbids business with Tamei species. The Torah forbids this. In Pesachim, we expound it from a verse. This applies to species destined to be eaten. A Gilyon in Tosfos says that the verse is only an Asmachta. Perhaps it is forbidden only when the Yisrael acquires them, but not if they are a mere security. We hold that a Yisrael does not acquire a security from a Nochri. However, it seems that Hagahos Maimoniyos (Hilchos Ma'achalos Asuros 8:8) forbids. He permits one who collected Tamei species for a debt to sell them, for this is like a hunter who chanced upon them. This implies that this is only if he already collected, lest he lose his debt, but l'Chatchilah one may not lend to them on such collateral. However, perhaps lending to them is more lenient. Perhaps [the Nochri will pay, and] the Yisrael will never get the Tamei species. R. Tam (in Tosfos Bechoros 2b DH Shema) forbids partnership with Nochrim only l'Chatchilah [lest the Nochri come to swear in the name of his idolatry]. If he already became a partner, he may accept the oath, to save his money. The Rashbam forbids accepting the oath. The Mordechai explains that since the Gemara forbade partnership l'Chatchilah, even b'Di'eved, he may not accept the oath. If so, according to the Rashbam, there is no proof from Hagahos Maimoniyos. Perhaps we are more lenient to lend l'Chatchilah. According to R. Tam, the reasoning is opposite. R. Shimshon (Shevi'is 7:3) says that Chachamim permitted only professional hunters. The Yerushalmi explains that this is because the government collects taxes. Even according to this, we can permit lending to Nochrim on Ribis using Temei'im for security, for the government collects taxes primarily due to loans with Ribis In any case it is repulsive for Yisre'elim to lend on security of swine. Maharam connotes that one may buy and sell Chelev l'Chatchilah, even if it is destined to be eaten. Tosfos forbids in this case. I wrote what seems to me.
Shulchan Aruch (YD 117:1): Anything that the Torah forbids, even if one may benefit from it, if it is special for food, one may not do business with it (Rema - or accept it for collateral), even to buy it to feed to one's Nochri workers. The only exception is Chelev, for the Torah said "it may be used for any Melachah."
Taz (1): The Beis Yosef brought from the Rashba that we forbid lest one come to eat them. This excludes a donkey or camel, which one raises for work. This is astounding. This is a Torah Isur. We learn from "Yihyu"! Tosfos (23a DH Amar) says that it is mid'Oraisa. It seems that the Rashba holds that this is why the Torah forbade, and it authorized Chachamim to decide what is permitted and wihat is forbidden, just like Melachah on Chol ha'Mo'ed (Chagigah 18a). Therefore, Chachamim forbade all food matters, lest one come to eat them. They permitted what is special for Melachah. Terumas ha'Deshen cites a Gilyon in Tosfos that says that it is only an Asmachta. I ask from Tosfos (Sukah 39a DH v'Leisiv), who says 'perhaps also buying in order to profit and resell it for more is called business, and Shevi'is 7:3 forbids business with Peros Shemitah, Bechoros, Terumos, Neveilos and Treifos. The only way we find that they are the same regarding [the Isur of] business is in this way (buying to resell for a profit), for the Torah explicitly permitted selling [if he did not buy it] - "Oh Mechor l'Nochri."' If the Isur of business is only mid'Rabanan, what is Tosfos' proof from Nevelah? There, surely the Torah permits! It is forbidden mid'Rabanan, and the Mishnah says that mid'Rabanan they are equal. I answer that Chachamim do not have the power to forbid what the Torah explicitly permitted. Therefore, Tosfos proved from the explicit Heter, that surely Chachamim did not forbid selling [what he did not buy in order to profit]. This must be permitted even mid'Rabanan.
Birkei Yosef (Shiyurei Berachah 2): People rely on this to raise talking birds (parrots) and animals to ride on (Maharikash). People rely on this to raise Tamei birds that sing (chirp) and similar things.
Birkei Yosef (6): If one bought a wormy food, Beis Hillel (84) forbids business with it. Pri Chodosh disagrees, for he sells the food, and not the worms!
Birkei Yosef (7): If one invested money with a Nochri, and the Nochri does business with Nevelos and Terefos, the Yisrael may receive a share of the profit.
R. Akiva Eiger (DH Asur): It is not clear whether or not one may have a fixed job cooking Isurim for a Nochri.
Tosfos Yom Tov (Shevi'is 7:3): In Bechoros, we say that even if milk were forbidden due to Ever Min ha'Chai, one may do business with it!
Pischei Teshuvah (1): Pri To'ar says that one may do business with blood, since the Torah equated it to water. Noda bi'Yehudah (2 YD 62) agreed. Chasam Sofer 106 added Ever Min ha'Chai, which is equated to blood. This answers the question of the Tosfos Yom Tov. Alternatively, we could say that the Isur of business is only mid'Rabanan (Chasam Sofer 108).
Shulchan Aruch (ibid.): If a hunter happened to catch Tamei Chayos, birds and fish (Rema - or one happened to get a Neveilah or Tereifah in his house), he may sell them, as long as he does not intend for this.
Rema: He must sell it immediately. He cannot wait to fatten it. Similarly, one may collect a loan from Nochrim from Tamei species, for this is like saving from them (if not, perhaps he would never collect at all). One may not sell to a Nochri a Nevelah in the guise of a Kosher animal. See CM 228:6.
Shulchan Aruch (ibid.): One may do business with anything forbidden only mid'Rabanan.
Beis Yosef (DH Kasav): The Yerushalmi forbids doing business with Isurei Torah, and permits with Isurei mid'Rabanan.
Shach (14): This includes brine of Nochrim. The Yerushalmi explicitly permits. Even though it was forbidden because they mix in wine (Tur 114:11), and Stam wine of Nochrim is Asur b'Hana'ah (Shulchan Aruch 123:1), we can say that they do not sell more brine due to the wine. Also, one can sell it except for the value of the wine inside, like the Tur (134:2) and Rema (124:23) say.