The same holds with nutrition. Even if we grant that veins may obtain their nutrient blood by virtue of the _horror vacui_ (chap. i.), how could this explain the nutrition of nerves? Erasistratus's hypothesis of minute elemental nerves and vessels within the ordinary visible nerves simply throws the difficulty further back. And is Erasistratus's minute "simple" nerve susceptible of further analysis, as the Atomists would assume? If so, this is opposed to the conception of a constructive and artistic Nature which Erasistratus himself shares with Hippocrates and the writer. And if his minute nerve is really elementary and not further divisible, then it cannot, according to his own showing, contain a cavity; therefore the _horror vacui_ does not apply to it. And how could this principle apply to the restoration to its original bulk of a part which had become thin through disease, where more matter must become attached than runs away? A quotation from Erasistratus shows that he did acknowledge an "attraction," although not exactly in the Hippocratic sense. Chapter VII In the last resort, the ultimate living elements (Erasistratus's _simple vessels_) must draw in their food by virtue of an inherent attractive faculty like that which the lodestone exerts on iron. Thus the process of anadosis, from beginning to end, can be explained without assuming a _horror vacui_. Chapter VIII Erasistratus's disregard for the humours. In respect to excessive formation of bile, however, prevention is better than cure: accordingly we must consider its pathology. Does blood pre-exist in the food, or does it come into existence in the body? Erasistratus's purely anatomical explanation of _dropsy_. He entirely avoids the question of the four qualities (_e.g._ the importance of innate heat) in the generation of the humours, etc. Yet the problem of blood-production is no less important than that of gastric digestion. Proof that bile does not pre-exist in the food. The four fundamental qualities of Hippocrates and Aristotle. How the humours are formed from food taken into the veins: when heat is in proportionate amount, blood results; when in excess, bile; when deficient, phlegm. Various conditions determining cold or warm temperaments. The four primary diseases result each from excess of one of the four qualities. Erasistratus unwillingly acknowledges this when he ascribes the indigestion occurring in fever to _impaired function_ of the stomach. For what causes this _functio laesa_? Proof that it is the fever (excess of innate heat).