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is a common source of nutrition for the whole body; a single centre of circulation. Hence all parts are immediately dependent, for the means of their nutrition and growth, and for the materials of their various exertions, on the digestive organs and the circulating system. There is a common point, to which all sensations proceed, and from which volitions emanate; the seat of the inferior propensities, of the moral feelings, and of intellect ; the source of nervous energy. The nervous sys- tem, of which the central portion executes these important offices, associates the actions of the va- rious apparently distinct organs, and combines them for the common purposes of the economy. It regulates the combination and succession of movements, making them orderly and harmonious, so that, although the multiplicity and intricacy of parts seem endless, the machinery works silently and imperceptibly. ‘This system is the great in- strument of co-operation and sympathy ; by means of it the various parts work together in health, and suffer together im disease. Hence the expression of Hippocrates, in reference to the human body, is strictly correct, “ Labor unus, consentientia omnia.”
Again, although individual organs are numerous, the elements of organic structure are few. The various proportions, in which they are combined, make the difference; as the various combinations of a few letters produce the infinite variety of �
