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] X