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Norz XXXVII, VEGETABLE RESPIRATION. 449

to be termed perſpiratory organs as leaves. Others have believed them excretory organs of excrementitious Juices; but as the vapour exhaled from vegetables has no taſte, this idea is no more probable than the other; add to this that in moiſt weather, they do not appear to perſpire Or exhale at all.

The internal ſurface of the lungs or air-veſſels in men, 15 ſaid to be equal to the external ſurface of the whole body, or about fifteen ſquare feet; on this ſurface rhe blood is expoſed to the influence of the reſpired air through the medium however of 2 thin pellicle; by this EXpolure to the air it has its colour changed from deep red to bright ſcarlet, and acquires ſomething ſo neceſlary to the exiſtence of life, that we can live lcarcely a minute without this wonderful proceſs.

The analogy between the leaves of plants and the lungs

or gills of animals ſeems to embrace lo many circu ſtances, that we can ſcarcely withhold our

performing ſimilar offices.

1. The great ſurface of the leaves compared to that of the trunk and branches of trees 1s ſuch, that it would ſeem to be an organ well adapted for the purpoſe of ex- Poſing the vegetable juices to the influence of the air; this however we ſhall ſce afterwards is probably performed only by their Upper ſurfaces, yet even in this caſe the ſur- face of the leaves in general bear a greater Proportion to the ſurface of the tree, than the Iu external ſurfaces.

m- aſflent to their

ngs of animals to their

2. Inthe lungs of animals, the blood after having been expoſed to the air in the extremities of the pulmonary PART 1. Gg