PARTS OF ANIMALS, III. v. 



which this material is carried. As regards the 

 manner in which animals are nourished, the source 

 of the nourishment, and the processes by which 

 they take it up from the stomach, it is more appro- 

 priate to consider these subjects and to discuss them 

 in the treatise on Generation. 



[But since the parts of the body are composed 

 out of blood, as has been said, it is easy to see why 

 the course of the blood-vessels passes throughout 

 the whole body. The blood must be everywhere 

 in the body and everywhere at hand if every one of 

 the parts is constructed out of it.] ** 



The system of blood-vessels in the body may be 

 compared to those water-courses which are con- 

 structed in gardens : they start from one source, 

 or spring, and branch off into numerous channels, 

 and then into still more, and so on progressively, so 

 as to carry a supply to every part of the garden. 

 And again, when a house is being built, supplies of 

 stones are placed all alongside the lines of the 

 foundations. These things are done because (a) 

 water is the material out of which the plants in the 

 garden grow, and (6) stones are the material out of 

 which the foundations are built. In the same way, 

 Nature has provided for the irrigation of the whole 

 body with blood, because blood is the material out 

 of which it is all made. This becomes evident in 

 cases of severe emaciation, when nothing is to be 

 seen but the blood-vessels : just as the leaves of vines 

 and fig-trees and similar plants, when they wither, 

 leave behind nothing but the veins. The explana- 

 tion of this is that the blood (or its counterpart) is, 

 potentially, the body (that is, flesh — or its counter- 

 part). Thus, just as in the irrigation system the 



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