Anatomical Observations on the Lungs

...is not driven by a continuous motion, but as if by alternating impulses; fluctuating, it moves forward and backward at the same time through the same path, which also happens when the heart and the auriclethe upper chamber of the heart have been removed.

From these observations, to resolve the first problems by the analogy and simplicity which Nature uses in her works, one can conclude that the network—which I previously believed to be nervous, mixed among the vesiclesthe tiny air sacs of the lungs, now called alveoli and their boundaries—is actually the vessel that carries the blood-like substance in or out. Although in the lungs of more perfect animals original: "perfectorum animantium"; Malpighi refers to mammals as "perfect" compared to "imperfect" amphibians like frogs., it sometimes seems that a vessel ends and gapes open in the middle of the rings of the network, it is nonetheless probable—just as happens in the cells of frogs and tortoises—that this vessel has even smaller vessels extended further in the manner of a network, which, on account of their extreme smallness, escape even the most careful sight.

From these things also, with the highest probability, the problem concerning the mutual union and anastomosisa connection or opening between two things that are normally diverging or branching, such as blood vessels of vessels can be solved. For if Nature once willed the blood to remain within vessels and blends the ends of the vessels into a network, it is probable that she joins them by anastomosis in other cases as well. This is clearly detected in the bladder of frogs when distended with urine, in which the swift motion of the blood is observed through transparent vessels joined to one another by mutual anastomosis; indeed, these vessels have attained that connection and progression which the veins or fibers in the leaves of almost all trees constantly trace out.

To what end all these things are done—beyond those matters I touched upon in my previous letter regarding the pulmonary mixtureoriginal: "pulmonaria miscella"; refers to the mixing or interaction of air and blood in the lungs—you yourself seem to have understood perfectly. Nor should your own most celebrated discovery be withheld, which you shared with me in the letters written out of your kindness, in which you philosophized subtly by observing the wonderful marvels of Nature in plants. We marvel that apples hang from a trunk not their own, and that the pleasant "adulteries" of plants A 17th-century metaphor for grafting different species together. have introduced illegitimate offspring onto legitimate births by a delightful mixture. For we see one and the same tree take on different characters in its branches: while here the hanging fruits entice the taste with a pleasing acidity, there they delight with a nectar-like sweetness...