Bodleian Library MS. Barocci 131

+ Concerning mixture

In the definition of digestion, that it acts upon food slowly is clear to all, as are the inversions of the theorems. But it is necessary to return again to the principles, so that the subject before us may become more clear to you. Galen says, therefore, that all bodies under the moon that undergo generation and corruption are mixed from the four elements: namely earth, water, air, and fire. From fire and air, then, living beings possess their vital and sensory power; and from earth and water, they possess the nutritive and augmentative power. Since, then, living beings are mixed from the four elements, it is necessary for them to be nourished and to grow by similar things. But since the elements are simple, while the bodies of living beings are composite, it was not possible for the simple to be nourished by the simple. On this account, Nature devised food, so that through it the composite bodies might be
+ Concerning food

nourished. Since food is not immediately of the same nature as the living being, Galen says that food is like the nature of the living being in potential and suitability, but in actuality and essence, it is foreign. In order, therefore, that food, which is foreign in essence, may become akin in essence, it requires digestion. For digestion is nothing other than an alteration of the food into the nature of the thing being nourished. Since Nature cannot immediately and all at once change food into its own power, for this reason Nature devised the stages of digestion: first, the one in the stomach, which is the one properly called digestion; second, the one in the liver; third, the one in the vessels; and fourth, the one in each part. And the digestion in the stomach, and that in the liver, and that in the vessels, are not simply digestions, but are preparatory for the digestion in each part. For the digestion in each part is the proper and most sovereign digestion.
+ Digestion

For this assimilates the food to the part being nourished. But the digestion in the stomach does not assimilate the food to the living being, but only prepares it, so that it may more easily be changed by the digestion in the liver. And the digestion in the liver, even this does not assimilate the food to the living being, but only makes it blood. And blood is neither flesh, nor nerve, nor bone, but the nourishment for these. The digestion in the vessels, even this does not assimilate the food to the living being, but only prepares it for the digestion in each part. But the digestion in each part—this is the proper digestion, which also assimilates the food to the part being nourished. And this digestion is not simple, but twofold: for one part is alteration, and the other is addition. And alteration is the change of the food into the essence of the part being nourished, while addition is the application of the food to the part being nourished. And alteration precedes addition, while addition follows alteration. And alteration occurs through the alterative power, while addition occurs through the attractive power. Since, then, digestion is the alteration of food into the nature of the nourished being, and this alteration occurs through heat, on this account Galen includes heat in the definition of digestion. For he says that digestion is the alteration of food into the nature of the nourished being, brought about by the innate heat. And since innate heat is not simple, but is mixed from heat and moisture, for this reason digestion also is not simple, but is mixed from heat and moisture. And heat is that which acts upon and alters the food, while moisture is that which receives the alteration. And heat is that which effects the digestion, while moisture is the matter of the digestion. And heat is that which enacts the digestion, while moisture is that which undergoes the digestion. And thus digestion occurs through innate heat and moisture.