Whether bile [fel] is only a superfluity.
The disposition, then, follows in this manner," etc. Here the Philosopher makes a determination regarding the parts of bloodless animals. And this is why one inquires for the first time in Book Fourteen whether or not bile [fel] is only a superfluity.
1. And it seems not. Because every member is generated from something like it, from which it is established in its complexion and essence. But there are many choleric members. Therefore, they are nourished by something choleric. But bile is such a thing, and therefore, etc.
2. Furthermore, everything that is produced as a result of nature operating in an ordered manner [ ordinate] is produced for the sake of something. But four humors are generated in the stomach from chyle, which are necessary for living beings. But one of these humors is contained in the gall bladder. Therefore, bile is necessary.
The Philosopher says just the opposite and criticizes Anaxagoras for saying the opposite.
One must respond that choler [ cholera] is of two types, since one is necessary and the other is helpful. And the necessary is also of two types: universal and particular. The universal is for the sake of the choleric members, and the particular is for the sake of the gall bladder. The helpful sort is also of two types: one is universal, and flows in the body with the blood, and the other is particular, and runs to the bottom of the stomach in order to promote digestion.
Thus, when one asks whether bile is only a superfluity, one must respond that it is, because that choler that mixes with blood through the power of nature that cleans the blood is sent to the proper receptacle, that is, to the gall bladder. Thus bile is a superfluity of the choler flowing with the blood.
(1-2).The first argument proceeds concerning the choler, which is outside the gall bladder and out of which the choleric members are nourished. And one must respond in like manner to the second argument, and the Philosopher does not speak about this. This is why, etc.
Whether some of the bile or choler is naturally sent to the intestines.
One asks further whether some of the bile or choler itself is naturally sent to the intestines.
1. And it seems not. This is because not only expulsion is necessary to the digestive power, but retention is also necessary. Now expulsion is through the hot and dry, whereas retention is through the cold and dry. But none of the black bile [melancholia] is sent to the intestines for the sake of retention, and therefore neither is any of the choler sent for the sake of expulsion.
2. Moreover, a light humor naturally rises up. But of all the humors choler is the lightest. Therefore, it will not naturally descend nor will it be sent to the intestines.
The opposite is clear according to the Philosopher's determination. For he says that the intestines of choleric ones are bitter. But this is due only to the admixture of bile.
One must respond that nature sends choler to the intestines because digestion does not advance unless the expulsion of impurities follows. Now, then, the expulsive power operates with the mediating influence of the hot and the dry, and bile and choler are sent to the intestines in order to expel the impurities more easily.
1. To the first argument one must respond that the intestines do not require the retention of impurities, but rather their expulsion, and this is why the intestines do not need black bile. And, moreover, for this reasonbecause the intestines are naturally cold and drythey therefore have sufficient power of retention on their own without the assistance of black bile.
2. To the second argument one must reply that nature works according to the intention of the end, and not according to the intention of the material. But now it is the case that heat is the principle of digestion, and the cold and the dry are the cause of appetite, and this is why black bile is sent to the opening of the stomach, in order to promote or arouse the appetite, but choler is sent to the bottom of the stomach in order to promote digestion.
-  Throughout this book A. uses both fel and cholera where we would likely use only the term "bile." As an aid to the reader, we have sought to keep the two distinct.