How, then, could blood ever turn into bone, without having first become, as far as possible, thickened and white? And how could bread turn into blood without having gradually parted with its whiteness and gradually acquired redness? Thus it is quite easy for blood to become flesh; for, if Nature thicken it to such an extent that it acquires a certain consistency and ceases to be fluid, it thus becomes original newly-formed flesh; but in order that blood may turn into bone, much time is needed and much elaboration and transformation of the blood. Further, it is quite clear that bread, and, more particularly lettuce, beet, and the like, require a great deal of alteration in order to become blood.
This, then, is one reason why there are so many organs concerned in the alteration of food. A second reason is the nature of the superfluities.[59] For, as we are unable to draw any nourishment from grass, although this is possible for cattle, similarly we can derive nourishment from radishes, albeit not to the same extent as from meat; for almost the whole of the latter is mastered by our natures[60]; it is transformed and altered and constituted useful blood; but, in the radish, what is appropriate[61] and able of being altered (and that only with difficulty, and with much labour) is the very smallest part; almost the whole of it is surplus matter, and passes through the digestive organs, only a very little being taken up into the veins as blood—nor is this itself entirely utilisable blood. Nature, therefore had need of a second process of separation for the superfluities in the veins. Moreover, these superfluities need, on the one hand, certain fresh routes to conduct them to the outlets, so that they may not spoil the useful substances, and they also need certain reservoirs, as it were, in which they are collected till they reach a sufficient quantity, and are then discharged.
Thus, then, you have discovered bodily parts of a second kind, consecrated in this case to the [removal of the] superfluities of the food. There is, however, also a third kind, for carrying the pabulum in every direction; these are like a number of roads intersecting the whole body.
Thus there is one entrance—that through the mouth—for all the various articles of food. What receives nourishment, however, is not one single part, but a great many parts, and these widely separated; do not be surprised, therefore, at the abundance of organs which Nature has created for the purpose of nutrition. For those of them which have to do with alteration prepare the nutriment suitable for each part; others separate out the superfluities; some pass these along, others store them up, others excrete them; some, again, are paths for the transit[62] in all directions of the utilisable juices. So, if you wish to gain a thorough acquaintance with all the faculties of Nature,[63] you will have to consider each one of these organs.
Now in giving an account of these we must begin with those effects of Nature, together with their corresponding parts and faculties, which are closely connected with the purpose to be achieved.[64]
[XI]
Let us once more, then, recall the actual purpose for which Nature has constructed all these parts. Its name, as previously stated, is nutrition, and the definition corresponding to the name is: an assimilation of that which nourishes to that which receives nourishments.[65] And in order that this may come about, we must assume a preliminary process of adhesion,[66] and for that, again, one of presentation.[67] For whenever the juice which is destined to nourish any of the parts of the animal is emitted from the vessels, it is in the first place dispersed all through this part, next it is presented, and next it adheres, and becomes completely assimilated.
The so-called white [leprosy] shows the difference between assimilation and adhesion, in the same way that the kind of dropsy which some people call anasarca clearly distinguishes presentation from adhesion. For, of course, the genesis of such a dropsy does not come about as do some of the conditions of atrophy and wasting,[68] from an insufficient supply of moisture; the flesh is obviously moist enough,—in fact it is thoroughly saturated,—and each of the solid parts of the body is in a similar condition. While, however, the nutriment conveyed to the part does undergo presentation, it is still too watery, and is not properly transformed into a juice,[69] nor has it acquired that viscous and agglutinative quality which results from the operation of innate heat;[70] therefore, adhesion cannot come about, since, owing to this abundance of thin, crude liquid, the pabulum runs off and easily slips away from the solid parts of the body. In white [leprosy], again, there is adhesion of the nutriment but no real assimilation. From this it is clear that what I have just said is correct, namely, that in that part which is to be nourished there must first occur presentation, next adhesion, and finally assimilation proper.
Strictly speaking, then, nutriment is that which is actually nourishing, while the quasi-nutriment which is not yet nourishing (e.g. matter which is undergoing adhesion or presentation) is not, strictly speaking, nutriment, but is so called only by an equivocation. Also, that which is still contained in the veins, and still more, that which is in the stomach, from the fact that it is destined to nourish if properly elaborated, has been called “nutriment.” Similarly we call the various kinds of food “nutriment,” not because they are already nourishing the animal, nor because they exist in the same state as the material which actually is nourishing it, but because they are able and destined to nourish it if they be properly elaborated.
This was also what Hippocrates said, viz., “Nutriment is what is engaged in nourishing, as also is quasi-nutriment, and what is destined to be nutriment.” For to that which is already being assimilated he gave the name of nutriment; to the similar material which is being presented or becoming adherent, the name of quasi-nutriment; and to everything else—that is, contained in the stomach and veins—the name of destined nutriment.