In short, digestion prepares the nutritive or vital matter, which is taken up by absorption--the first of the simple nutritive functions; respiration renovates it in the very middle of its course--between the two portions of the simple function of circulation; and generation, dependant on secretion--the last of these functions, communicates this nutritive matter, or propagates vitality to a new series of beings. In such arrangement, the digestive organs, therefore, precede, and the generative follow, the simple nutritive organs; while the respiratory occupy a middle place between the venous and the arterial circulation. Nothing can be more improper, as the preceding observations show, than considering any one of these as a distinct class. More fully, therefore, to enumerate the nutritive or vital organs, we may say, that, under them, are classed, first, the organs of digestion, the external and internal absorbent surfaces, and the vessels which absorb from these surfaces, or the organs of absorption; second, the heart, lungs, and bloodvessels, which derive their contents (the blood) from the absorbed lymph, or the organs of circulation; and third, the secreting cavities, glands, &c., which separate various matters from the blood, or the organs of secretion, and of which generation is the sequel. [24] Appendix E. [25] In perfect consistency with the assertion, that, though the organs of digestion, respiration, and generation, were really compound, still they were chiefly nutritive or vital, and properly belonged to that class, it is not less remarkable, that, in this division of the body, they are found to occupy that part, the trunk, in which the chief simple nutritive organs are contained. This also shows the impropriety of reckoning any of these a separate system from the vital. [26] The bones resemble these, in containing the greatest quantity of earthy mineral matter. [27] It is the possession of vessels which constitutes the vitality of vegetables. [28] In animals, alone, is nervous matter discoverable. [29] Plants have no real circulation, nor passage of their nutritive liquids through the same point. [30] This arrangement of anatomy and physiology was first published by me in 1806; and, notwithstanding its being the arrangement of nature, it has not been adopted by any one that I know of, until very lately, when it was in some measure used by Dr. Roget, without acknowledgment. The originality, as well as the truth and value, of this arrangement, will be illustrated by referring to any other published previous to 1806, or even to 1808, when I republished it in "Preliminary Lectures," Edinburgh.